Experimented with plastic milk bottles: they don't gush if I keep the cap on and trickles to the bottom if there's not much liquid. I used sandstone pebbles so it may be a different story with punchier ammo.
Shooting the neck off a beer bottle is a bit cliched but someone will have to do it. Shooting the neck off so it pours into a glass; now there's exciting.
One pint tetrapak of milk shot into poring milk into a bowl of cereal...
But for now I hope to film an egg cracked open with catapult ammo so that it's contents fall into a frying pan heated on a wood gas stove. Might be a week before I get the opportunity. I've done it once so I know it's quite straight forward.