Indispensable is a strong adjective for something that you couldn't do without. If you have asthma and you're packing for summer vacation, your inhaler is indispensable, unless you enjoy gasping on the beach.
Something that is dispensable is something you could get rid of, like that box of yogurt-covered zucchini snacks that's been in the pantry for a year. So if something is indispensable you couldn't possibly go without it, like salt, or for some people, coffee. Chocolate is indispensable for chocolate chip cookies, as is furniture for the adult hide-and-go-seek league.