I think you already answered this, but doesn't hurt to ask. What exactly is the difference between an ita bag and a normal bag? Also what exactly is an ita bag?
The term “ita-bag” (痛バッグ) literally means “painful bag,” which references both the pain inflicted on the bag by having so much merch on it and the pain inflicted on the owner’s wallet. This trend started a while back in Japan, but recently picked back up over there and has come full circle to fans over in the U.S. and other Western countries. They’re basically used to show support for a certain character, ship, or fandom you love, and most people bring theirs out at cons (hence why I’m showing mine off at Blizzcon and future cons I attend).
The difference between a normal bag and an ita bag is that ita bags are supposed to have open windows you can display keychains/charms and buttons, that way people can see them clearly. Here are some examples of common ita bags people usually buy:
I’d say I’ve shoveled a little over $200 into my ita bag by buying merch from friends, having it given to me by kind people, and buying a fuckton of it at Anime Expo. I save up for cons or for merch I spot online, and buy whatever I can add to my bag.
Some people have multiple bags, either for the same ship/character/fandom or for different characters/ships from different fandoms. It’s not unusual, for example, to see someone have two different McHanzo bags and have a third for, let’s say, DVa by herself. Again, the more bags you have, the more expensive it is because every time you see merch, you think to yourself, “I NEED IT FOR MY BAG!”
It’s really fun to show your love for your favorite ships or characters, though. And it helps you connect with other fans at conventions, because they usually stop you if they recognize the character(s) on your ita bag and strike up a conversation.
tl;dr It’s the equivalent of peacocks showing off their feathers to attract a mate, only fans use it to show off their love for a character/ship/fandom with the hopes of finding other fans like them.