each character got a tracker (from 1d2 to 1d20)

when they want to buy something, they roll

we don't need to know how much precise coins we got, just if they usually don't have a lot (1d2) or if they usually go outside with the bag often filled (1d20). On a miss, it can be stolen or just forget at home etc. Great idea to create twists and turns and avoiding counting your coins