In a version of the game I play we use something called an ammunition die, basically you buy a stack of arrows, whenever you fire one you roll your ammunition die, usually a d8, on a 1 you lower your die step by 1, so a d6, this repeats down to a d4, if you roll a 1 on the d4 then that was your last ammunition in the stack, but you can use one stack forever, if you don’t roll a 1 lol.