I bit inspired by the Walking Dead and Andre Norton's, The Last Planet (Star Rangers)!
Harry and his family decided it was time to leave. Voldy had started a war with the non magical. It led to a world wide bloodbath. The non magicals started using a variation of splaitergott to take down the magicals. Harry and his twenty three tried to save everyone. When Tom releashed a magical virus that turned non magical people into flesh eating Zombies. Many nukes were used on the continent, as that was Toms biggest recruitmenting spot. Whether it was the nukes, the magical Zombie spell or the viral splaitergott, both viruses spread to the other side. It was probably the Squibs as they were and were not magical. Harry and his were on the uncharted, unplottable Black island. The island held close to five hundred people and almost as many Elves. Many Squibs from 'Muggleborn' families, an entire company of 'Sport and Social' (Due to Mr Granger), and a number of young magicals and families of all three groups. About seventeen tried a Coup, it was put down with extreme prejudice. About thirty died or were critically injured.
The magicals had spent all their gold getting plants, animals, and ingredients for potions. The Goblins then found out, they were not immune. So their staying out of wizard business, ended them also. The magicals, elves, and SAS started on every warehouse district in the mundane world. They picked up about fifty more young people. Then they started on the magical districts. Books, tents, brooms, carpets, clothes, bags, and trunks as well as telescopes from the non magic stores. Much better than the magical ones. Hermione did the bookstores. Tonks the misc. stores and because of needing vision enhancement, the Ocular store. "Best get the meat and frozen stuff cleared out before the hydro dam electricity goes out and all that food goes to waste", Harry said peering down the street and taking in the many restaurants lining it. This was a huge restaurant street, many fast food and others in between exclusive and family run. Then Luna said, "so, I'm going to put a stasis charm on a huge expanded trunk and throw everything in there frozen," waving her wand toward a meat packing plant in the district they were raiding and Harry agreed. "And two others for you my dear. One for non cold, like condiments and other stuff, the other one stasis for refrigerated things."
"Hey, Hermione and Tonks, take Ron and Neville. Go find a couple of RV lots or something similar like dirt bikes and ATV's and shrink it all down. Maybe a Humvee type car lot as well. We can use stuff like that to travel, scouting, and housing as well for the non magicals," he said, making sure his gun and wand was handy.
"I'm going to hit that sporting goods store," said Charlie and Sasha, as they went to put words to action. Luna put in: "Get every type of weather gear, and hell, all the stuff. Like you said, we might need extra shelters or different weapons, like bows and fishing gear." Later after having several tens of thousand of tons of things they started on weapons and general sundries not kept in food areas. Harry made sure that they could get weapons to defend themselves from several military bases. They came across what they thought was an American base, but was a nursing school and storage facility. It was under attack by the zombies of death. There were a few magicals as well, healers and potion makers. They had been supplying the various centers as they went down one by one. Everyone was amazed at all the stuff they were getting from the storage facility as it was not sealed by magic. Everything went into the expanded bags and trunks. Another several hundred thousand tons.
Everything you could think of under the sun was flying into those containers all twenty had. If they played it right, they would have power, food, fuel, weapons (and how to downgrade them), and water. Everything they needed to survive was there. Even stuff for growing food, or feeding animals as fodder. Not to mention clothes, hygiene products, and other essentials that would come in handy later. It was the staging base of the resurrected 4077th Mobile Army Surgical Hospital. They picked up seventy-two nurses, nineteen doctors of surgery (MASH Docs), thirty more regular military, and seventeen healers and potion makers, none masters. The head military guy (Lt. Colonel Burns in charge) tried to take over, but the SAS who joined the nurses, and Magicals told him to stuff it. His wife kept him in hand, especially to save her children and grandchildren.
"Grab everything. Who knows what we'll need later," Susan Bones told all the leftover magicals, finally moving from where she had stood. Her face was a mask of determination. She knew what they were now. But stealing was not nice, didn't like it, but knew they might need it to survive. As they were emptying a shopping mall, they found forty-three minor school children and four teachers, assistant principal and school nurse with a few (ten) female employees and late teenagers that had been in the theater. The manager had closed the gate and was torn apart after locking it.
"Yeah, you're probably right. We can do the whole trucking district before morning. Then take a day to relax, then repeat, until all the bags, trunks, etc. are filled. Or not, we'll see how the trucks and truckstops pan out. We might have to do more tomorrow," Harry warned, getting nods from the rest of the group.
Harry and the other magicals started the ritual that would put them into another world that would be safer for them. Everyone was inoculated for the plagues. It had taken a year; with over a hundred children and elderly dying. Mostly under five for non magical children and for magicals those over child bearing age (fifty or so). So Prince Lord Harry Potter-Black-Bones-Dagworth-Granger-Emrys-Gryffindor-Pendragon-Peverell-Slytherin and his wives and followers left this earth thru a hermetically sealed portal. The area was warded, so none of the diseases could go thru. When finished, the portal and island would be flash-fired clean.
Lady Bones was is charge of the magical fighter/scavenger force. Andromeda Tonks (healers), Major Margaret Pierce (nurses), and Major Hawkeye Pierce (doctors and surgical staff) were in charge of the medical. Major Lord Smith was in charge of the (non medical) SAS and regular military. Lady Luna Peverell was in charge of the animals (with Lord Charlie and Lady Sasha Prewett) and intelligence (as a type of seer). Lady Hermione Dagworth-Granger was in charge of spell research and preparing for missions with Luna's help.
Lady Dora Tonks-Black was in charge of policing everyone. Lord Neville and Lady Hannah Longbottom were in charge of all plant life. Lord Ronald and Lady Lavender Brown were in charge of entertainment and refreshments. Lord Bill and Lady Fleur Weasley are in charge of warding and shielding. Lord Fred Spinnet and Lord George Johnson were creators of just about anything. They helped in Research and entertainment, as well as weapons. Lord Lee Jordan was propaganda. Angelina Johnson and Alicia Spinnet were learning healing under Andromeda Tonks. Katie Bell help in transportation as she knew about Brooms and mechanical vehicles. Ted Tonks was Law and surprisingly interrogation.
Besides Harry; the twenty-three that were not lords and lady's then were the following. Hermione, Dan, and Emma Granger; Ron Weasley; Lavender Brown; Bill and Fleur Weasley; Charlie and Sasha (Prewett) Weasley; Luna Lovegood; Susan Bones; Neville Longbottom; Augusta Longbottom Nee Brown, Hannah Abbott; Nymphadora (Dora) Tonks; Andromeda and Ted Tonks; Fred and George Weasley; Alicia Spinnet; Angelina Johnson; Katie Bell; and Lee Jordan.
The set up was to be temporary. The reason was all the celebrity mansions that could be turned into impregnatable castle strongholds. They levitated a children's camp from Shasta County, California. They spent the next week setting up the campsite. They wanted to make sure that it would host both non-magical and magical. Since this was an established campground for a kids environmental class. Which usually was two weeks long. It had Cabins for eight fifth grade students and a side room for the counselor. Ten of these, then ten shower bathrooms five for each sex. The magicals made sure to rig them with runes to never run out of water and stay a tepid temperature, to keep from using electricity to power them. The toilets had runes in the bowl to banish waste. The RVs were spelled the same way. And a huge dining get together space.
There was a water reservoir that was also spelled too never empty. Rain would still fill it, but with runes it would never let it get below a certain spot. Water was not something they would ever run out of. If the reservoir, for whatever reason, was destroyed, they all knew the water spell and could make another. Well, the magicals could anyway.
The RVs and regular tents were set up for the civilian side and military tents for the others. They didn't want to put non-magicals in magical tents, for there were things in magical tents that non-magicals couldn't use. It was just simpler to give them what they were comfortable with.
Meals would be communal. They expanded the cafeteria for the site. It was a good thing it was Fall. The elves were in charge of the food. Cooking, storing and dispersion. The people would be able to 'purchase' snacks and stuff, but main meals were group interactions only. This way food could be regulated and kept track of.
They decided to see what was going on in the city. They were all surprised that no magicals had come from all the magic to see if anything was going on. They found a city that was so technical, that Hermione was having a fit. They found a small tribe of people that were the remnants of a highly advanced space civilization. Over half were telepaths. The three groups integrated. The books that were brought set their new people into the mid eighteen hundreds as far as technology goes. The few people in the city, wanted nothing to do with them.