I have 2 small hob filters (whisper and tetra second nature, good size for 10-20 gallon tanks), a couple air pumps, and one sponge filter lying around.
I also have a couple round sponges that will fit over the hob intakes if you need them covered, as well as provide more biological filtration.
No small heaters, my only 10 gallon is a QT tank with a 150w heater, everything else is 29 and up.
I also have Najas indica (aka guppy grass) available, very useful for establishing new setups. Fast-growing plants like Najas are also helpful for maintaining water quality between partial changes, as well as supporting micro-critters that tiny fry will feed on.