Take the tabasco from the MRE and pour it on the heater. Then put water on the heater so it heats up the tabasco. It pretty much creates aroma that burns the eyes and gags everyone.
Also... MRE Bomb
Take a bottle, take the powder stuff out of the heater and put it in the bottle. Fill the bottle up halfway and close it tight. Eventually the heat and gas will expand the bottle and it will "pop", it can be kinda loud but it's pretty much harmless. Just gotta look out incase the hot water sprays out or the cap goes flying (which can happen if it wasn't tight enough).
Tabasco Sauce Tear Gas Bombs
Someone else posted a similar suggestion for MRE heaters and 2 liter bottles a while back - but they also included the warning to stay far back from it because they didn't and got hit with shards of plastic from the bottle. Also, be careful because setting one of these things off in your neighborhood could be construed by your neighbors (and the authorities) as something much worse than you think it is.