I just discovered a nifty idea for the painstaking task of tracking ammunition: The ammo die. The quick and dirty is that you roll a specifically sized die based on the general allotment of arrows, bullets, etc that you have. If you roll a Nat One on this special die, then you downgrade the Ammo Die by one size factor (a d20 decreases to a d12, etc) If you're on a d4, and roll a Nat One, then that was your last arrow.
This site explains the process more in depth.
This site explains the process more in depth.
