in junior high, i had a pretty common looking backpack - a dark green jansport. i had a few things hanging off it (keychains and such) that made it mine, but not a ton.
most lunch periods, i would hang out in the science classroom, playing othello with some other kids. i know, that's dorky enough on its own. usually i would dump off my backpack in the classroom and leave it there until my last period, which was science. i guess i had PE 5th period and didn't need my backpack or something. then i would go stright to catch my ride, and not stop by my little locker in homeroom.
so one day, when i got home, i go into my backpack and realize that it's not mine. it wa teh exact same green jansport... but wait. there's no keychains! i look at the papers inside and figure out that it's some guy's... i didn't even know who he was. i freaked out, but as i thought about it, i recalled possibly locking my backpack up that day for some reason. and i must have grabbed this one out of the classroom without thinking.
so what did i do?
the next day, i ran to the science classroom first and replaced the backpack. heart pounding, i ran back to my homeroom and unlocked my locker - my backpack was in there, thank god. i hadn't been sure. and i never spoke a word of it to anyone. that poor boy must have thought he was going crazy!
(p.s. i got out of the homework i'd missed because of a family emergency that randomly happened on that night - i was lucky in that way.)