A 2 liter bottle, pool cleaner (Hydrochloric acid), and shredded aluminum foil! Cap, shake, and toss... FAR AWAY....
Makes Hydrogen gas.... BOOM!
Did this at a friends house when I was a kid. Big fireball and took a huge chuck of grass out of the lawn.
*if you are dumb enough to try this, I will not be held accoutable for the consequences....