If you have a container with a small enough opening you can stretch a balloon over the vinegar/baking soda mix really fast and capture the CO2 that's produced. Depending on how much stuff you're using it could make it pop or fly off, fun either way.
back when dinosaurs roamed the earth, remco toys produced and sold a selection of modular 'science kits' packaged in cardboard cylindrical containers very similar in size to those commonly filled with quaker oats.
somehow i managed to acquire the one with which a kid could build a genuine working rocket. it consisted of the aforementioned rocket which--according to the instructions--was intended to be partially filled with vinegar (like up to the line) and a base/launch pad designed to accept a measured amount of baking soda.
there was also a rubber o-ring which hadda be installed for proper sealing. the base hadda lever-type trigger. according to procedure, after mating the rocket to the base, one was to shake the assembly once or twice and then place it in an open outdoor area, countdown from 10, press the trigger upon reaching 0 and then marvel as it blasted off into the 2-story-or-thereabouts-osphere.
as with all good things, the magic began to fade after a series of successful launches and that's when the real science began.
over the course of about an hour, we began increasing the amounts of fuel, countdown time and, having filled our notebooks with observed data, more fuel and longer countdowns combined.
as i sink further into the rapidly expanding morass that was once my memory, i'm no longer able to remember exactly how much more baking soda, vinegar and reaction time it took but i still vividly recall the historic moment when my associates and i invented the ied.
