Most of my friends instant cameras only take 10 pictures at a time. Do all instant cameras do this? If so, how many films should I buy?
Do all instant cameras only hold 10 pictures at a time?
Practically speaking, yes. All the instant cameras that most people would be likely to buy today use packs of 10 exposures.
Your friends likely have cameras that use Fuji Instax film cartridges, and those packs each contain ten pieces of film, or instant photos, or whatever you want to call them. There's a competing format called Polaroid Zink, but the paper for Zink cameras also comes in packs of 10 sheets.
The older, iconic Polaroid instant cameras like the OneStep cameras use film packs with only eight exposures per pack. Film packs in this format are still being produced by Impossible, so technically the answer to your question is: No, some instant cameras hold only 8 pictures at a time. But due to the cost of the film (around $2.50 per exposure), it's not a format you'd probably choose just for casual use.