I just moved in my new house and found a load of stuff someone left behind, i be glad to return them to the rightfull owner, please let me know by message, just tell me what the items are and i will pass them on.
Some people leave behind stuff as a welcome to the new owner...sometimes it's a mistake. Hang on to it for a bit and if they don't come back or contact you, then consider it a nice house warming gift!
My first apartment had a beta pickle and a ton of music blocks in storage - I kept expecting them to come back for it and they never did... so yay pickle I guess.