The team looked at Reid's messenger bag as the last member of their team - never knowing what it carried, only that it helped Reid work his magic.
It started one day when one of the other teams decided Reid could go without his bag for the day. Reid didn't stop searching for it the rest of his shift. He didn't have anything incriminating but he needed his bag. When Reid found his bag behind the bathroom trash bin he wiped the outside off with sanitary wipes and cleaned it off and checked the inside to make sure he had all of the contents inside. He did so he let out a sigh of relief.
The next time his bag went missing, no one in the BAU knew what happened and Reid ended up at his desk sitting on the floor rocking himself and trying to breathe. He hadn't let his bag out of his sight for four months and the one moment he let it go, it went missing again. Garcia had brought it back to him around seven as she was leaving, mentioning that it was in the women's restroom that time. Reid sighed and wished people would just leave him alone - he didn't touch other peoples belongings at all.
The next and very last time anyone decided to touch Reid's bag was when Reid caught Hotch picking it up from under his desk six months after the bag officially went missing. He marched over to his desk and hissed, "What are you doing?"
Hotch raised an eyebrow and said, "I wasn't going to take it. I just had something to put in it and then I was going to put it back."
Reid eyed his boss and lover and asked, "And have you put the object in my bag?"
"I have and I was about to put the bag back under your desk."
"Give me the bag and I'll take a look."
Hotch handed the bag over like he was dealing with a hostage situation and he sort of was dealing with a hostage situation if the look Reid was giving him was any consolation. Reid flipped opened the top and glanced through the contents of his bag until he came upon an envelope. He opened the envelope and it was a card from Aaron. He opened the card, read it, then glanced at Hotch and said, "I love you Aaron. Always and forever."
That's all Hotch needed to hear. He pulled Reid into a deep kiss and a promise that his life just got a lot more interesting. The bag would be witness to many more occasions and not another person decided that the bag needed to be anywhere besides with Reid - that and they feared his fiance, Unit Chief Aaron Hotchner.