A/N: This will just be a collections of headcanons that I have. Please feel free to use these in your own stories and adapt them for you own stories. I'd love to read them, so feel free to tell me about your stories.
Luna and Neville
After the war, Luna and Neville both went back to Hogwarts to complete their 7th year. They started going out in the October of that year and stayed together all the way through it.
When the summer came, Luna expressed interest in travelling the world and studying Magizoology first hand, while Neville had been offered Professor Sprouts' job. They decided it would be in both their interests to separate and take different paths.
Neville stayed on at Hogwarts, filling the role of Herbology teacher and Head of Gryffindor House (McGonagall now being Headmaster). He was love by all the students and soon became a favourite professor. He offered help to all those that needed it and set up tutoring within Gryffindor House, for those who struggled with work like he used to. This was soon adopted in the other houses as well. Neville eventually became Headmaster after McGonagall and Hogwarts thrived under him. He fell in love with Hannah Abbott and the pair had two children named after Neville's parents. Alice was born in 2009 and Frank in 2017.
Luna travelled the world, doing everything she had ever dreamed of and more. She discovered many magical creatures during her time abroad. When travelling in Southern America, she met Rolf Scamander, another Magizoologist and the pair travelled together, eventually falling in love and marrying. They settled in the North West of England when she fell pregnant with the twins, Lorcan and Lysander, in 2008. When the boys were 10, Luna fell pregnant again, and she had a girl who she named after her mother, Lysa. When they were of an age to start school, Luna an Rolf decided they would continue travelling in Western Europe during school terms, taking their young daughter with them for most of the time. Rolf suggested the boys study at Durmstrang, so that they were always near by. Luna wasn't too thrilled with the idea, she wanted them to attend Hogwarts. Rolf himself had attended Durmstrang, but it was now under a different Headmaster, who, Rolf insisted, was wonderful. Luna eventually cracked, and the twins started Durmstrang. Xenophilius fell ill just after the twins finished their OWLs, so the family moved back to England. The twins finished off their education at Hogwarts and Lysa attended when she turned 11.