maybe try this: get a buttstock ammo holder (spandex, holds 5-6 shells) throw 2 #6's in for squirrels, rabbits, and the like. 2 BB's in for heavier game like coyote, and a slug in for things that bite back like bears n 2 leggers.
personally, I normally carry 2 #4lead's and 3 #4buck's in...