That would be the nightmare scenario, Barry! I returned to my car in the Adirondacks after a three day trip and there was mouse poop all over the car. There were a couple snacks in there, but they were untouched. It was like Animal House had a frat party and the exclusive activity was to see who could drop the most. Realized later that they had come in through the cabin air intake, so I put some grated metal in front of that, but....that was a real "I don't want to touch my own car" drive home. A little mouse poop here or there doesn't bother me, but....the volume...it was amazing.
As for the key fob, I never take it on the canoe trip with me, because I just know if I do I'll either destroy it or it will somehow end up at the bottom of the lake. Instead, I have a sneaky little hiding place on my car where I stow it.