In all seriousness Imbroglio, you have no idea what could have been stored in those cans. In F-16 units in the Air Force, we use those cans to store gloves and stuff that were used in Hydrazine spills. Hydrazine is a toxic rocket fuel that the F-16 uses for its emergency power unit. If there is a spill or the aircraft uses its EPU in flight, a thorough cleanup occurs and we frequently use those ammo cans until the equipment is disposed of properly.
We deal with some bad ass chemicals in the military and frequently use air tight cans to contain the immediate vapor. When those cans are disposed of, you have no idea where they'll end up, or if they are completely clean of the toxins that were contained in them.
I don't mean to scare you about this but I'm being totally serious. If symptoms continue, email me and I'll tell you how to tell if you've been exposed to hydrazine.