You can use some of the smaller commercial pyrotechnics cartridges such as confetti, glitter, colored smoke, mini-gerbs, etc. They use a low voltage current(12v) to set them off. The confetti and glitter cartridges would slightly change the altitude momentarily when set off. I would avoid the flame cartridges.
is based in Canada but has dealers in the US and UK.
If using any pyrotechnics, always read the Safety Data Sheet first. It lists the clearances for the effect so you don't set anything or anyone on fire.