You've made a bottle rocket (or ten) and a sparkler bomb, and now you want to put those empty plastic bottles to a new pyromaniacal use. With a little rubbing alcohol and a match, this video by io9's Esther Inglis-Arkell will show you how to make your own homemade rocket booster in a bottle.
The process is super simple. Pour some rubbing alcohol into the bottle and swirl it around so the entire inside is coated. Pour out the excess so all that's left are fumes. Now, all you have to do is light a match and hold it over the neck of the bottle and you have a small, contained explosion.
Per Esther's advice, it's definitely a good idea to have a fire extinguisher handy. If you don't have one, it's pretty easy to make your own with some stuff you probably already have lying around the house.
You can also start a fire with a water bottle, or ignite different chemicals in a large plastic container to make cool "whoosh" sound effects. If you have a glass jar, you can use it to make green flames with boric acid and antifreeze or this awesome jam jar jet engine, which is basically a smaller version of Esther's experiment, only it uses methanol instead of rubbing alcohol.