Too much assumption here IMO.
Actually, if you knew how much ammo weighed there sure as hell wasn't that much in that bag Rick left the station with. Did I miss there being a great big cache of ammo elswhere or them managing to pick up a bunch along the way?
95 rounds fired at cans is 95 rounds that will never be used for anything else. This is going on with, as far as I can tell, no idea as to when/to what extent/if at all those rounds can be replaced. As stated in my earlier post there should be at least 50 dry-fires for every live round.
Your importance list left out water, which trumps at least food, in the short term anyway. In a hostile situation you've only got evasion (staying hidden), fortification (somewhere you can't be reached) and defense (ability to fight back). Ideally you can keep the first or at least fall back to the second. If faced with the third and relying mostly on guns every last round could mean living or dying. A shooting line with people blasting away runs rather counter to that harsh reality. Maybe the writers aren't really wanting us to sweat the ammo situation at this point and can obviously write in any feast or famine scenario with ammunition at their whim but I just have a hard time watching all those rounds going off and not thinking "That seems pretty damn free-wheeling with such a valuable and (presumably) finite resource.".