OP - I gave up carrying a wallet in Thailand all together as it's just too easy for pickpockets to steal it, not to mention the chance that you'll get caught out in the rain at some point.
I keep my ID on my phone (in pictures) and my cards in a small ziplock bag and my money in my front pocket.
That being said (small compensation now, I know) you may as well write it off with a mai pen rai and just check back at the box from time to time if it has some sentimental value.
IF it does show up there, thank them graciously for a job well done (if it's a Thai policeman). Might help you later in another sticky spot as they'll remember the "gracious tourist".
ETA: Example: was swept up in a month-end motorcycle stop and fleece checkpoint and an officer I had treated well and thanked for helping saw me, took me to 1 side, let the others get fleeced then sent me on my way with a friendly smile.