I've had a roll of duct tape stored in the truck kit kind of melt and make a mess.
Also don't store batteries in your gear, even eneloops. Most electronics now a days uses soft power switches which have a tiny amount of drain so they are slowly using some battery life just sitting so you need to top off the charge from time to time. I've also had a couple NiMH leak (not eneloops yet, cheaper brands) so you run that risk also.