When I was tent camping a few years ago, I had a number of 1 pound Coleman propane bottles go for a stroll.
I have had some close calls -- recently my neighbor had someone tear off the fuel filler door on his toad and siphon the tank... which is ironic because my truck is sitting there, literally feet away, with three full cans of gas for the generator in the bed, and it stays untouched.
Of course, I've had garbage (camp trash and the sacks from my bag toilet) stolen out of the bed of my truck. The most notable was people pulling up right along my parked truck when I was buying some items at a gas station, the thieves jumping from bed to bed, throwing the refuse (I was using a cast-off appliance box for all my garbage) to their truck, then driving off like they are on a getaway from a Fort Knox robbery...