a common military anti boredom tool. produced when you take the mre heater and drop it into a half full, plastic canteen. as the canteen is air tight for chemical warfare purposes, the pressure will build until it explodes. not very devistating, but a very nice pop in the middle of the night!
"Why is Spc Dingleberry emptying all of those latrines?"
"yeah, he rolled an canteen grenade into Sgt tinydicks tent last night after he caught him having cyber sex with his wife."