Name something you can fill a balloon with?

Answer 1

if you mean a small balloon like those of birthdays, they can be filled with normal air like your breath or it can be filled with helium gas, as it's lighter than air and balloons will be floating in air

and if you mean balloons like huge ones used in trips and so on, they are also filled with helium but there's also heat generator to make helium more lighter thus increase the height to which your alloon float

Answer 2

Air, helium, water, carbon-dioxide, bromine, mud,

hydrogen, oxygen, carbon-disulfide, sand.