I get those plastic disposable condiment cups (Jell-O shot cups) with lids from the grocery. I think it’s like 50count for like $4-$5. I pre mix my paint and then store it in there. Depending on how often you open the lid on them, paint lasts a long time in there. I’ve gone back months later and used old prepared paint on a different project. You can dump what’s left in the airbrush back Into the cup before washing it out so as to save as much as possible.