The oddest find was in my wallet. We were at a major tourist place and went shopping at a huge outlet mall. I must have purchased something in over a dozen different stores, paying cash.
I get back to our hotel and decide to replenish my cash with more money we kept in the hotel safe. When I pulled my money out of my wallet to count how much I had left, there was a fifty dollar bill that I knew I hadn't had or wouldn't have gotten back as change. It was kind of stuck to a five dollar bill.
And what made it worse, is that because I had bought so much stuff, I had consolidated everything into a couple of bags and tossed out the sales slips when I did that. I knew that there was no way I was going to be going back to any of these outlet stores if there was a problem (distance and time was too much for a repeat). I remember looking at them and thinking it was one less then to try and keep track of and tossed them in the garbage along with the extra plastic bags.
I'm the kind of person who can't even stand to take a penny at the local stores. It drives me crazy, because if I do take one, then I have to remember to pay it back the next time I'm in the store. So, it is less stressful for me not to take a penny.
But the lack of sales slips meant there wasn't any way I could figure out where that fifty dollar bill might have come from, so I kept it and still feel guilty about 15 plus years later.