My husband dropped his retainer in a trash bucket full of paper, which his mom then took and dumped into the wood stove! Needless to say there was no way that retainer would fit again after being burned in the stove!
As for lost items, my daughters and I went to a local toy store to pick some things out for her birthday. Instead of a paper registry, the store had buckets they would give you and you would physically take the items you wanted and put them in the bucket and then your kid's family and friends could come and just pick something out of the bucket to buy your kid instead of having to roam the whole store. Well, while we were picking things out, my daughter had been carrying an item of her own from home, and I wish I could remember what the specific item was, but at some point it ended up in the bucket without our knowing. Soon after, my MIL went by the store to pick something out and recognized my daughter's toy in the bucket. The store knew it wasn't theirs, so she took it home (along with other things she bought) and wrapped it up and gave it to my daughter on her birthday. At first she was a little bummed to get a gift she already had (we still didn't realize hers was missing), but then we were all shocked when we found it was actually hers!
Another time, my MIL was searching her house for hours to find one of my daughter's shoes before I came to pick her up and she finally gave up and went to the fridge to get a drink and yep, there was the shoe, in the fridge! My daughter was about 3, so who knows what made her think that was a good spot to put it, but now whenever someone in the family loses something, we all say "Check the fridge!"