you probably don't have the sheer amount of utterly useless cosmetic stuff i have. most of it isn't even cosmetic, i just use it as cosmetic. i have a leaf blade sword because it was the only silvery sword i could find that didn't have a max hit of 60.
I have lots of cosmetic stuff, and lots of random items I might need for quests; ropes, spades, torches.
I keep all kinds of tools and quest items, and I haven't bought any extra bank space either.
Now I don't know why you would need that much bank space readily available, but I usually have enough space for anything I need to do - and if not, I just get rid of something that I've stopped using, e.g. some items I recently bought for a treasure trail. it's not as if there's a problem or anything.
Surprise Exam is the worst bullstuff ever, by the way.