I see where you're coming from with this suggestion, saying that some extra stuff should be given to the player in a very small percentage of success (gun ammo, pizza slices, medkits in hospitals, you name it). However this could counterbalance the need of carrying 3 medkits, the need of going into Ammu-Nation shops to buy a piece, and going into the fast-food businesses to buy something to heal yourself. I really like this idea because it can be very equal to the real world somehow, you ask for the money with the gun pointing into the poor worker and he gives you money and something else somehow, BUT I just think this can be "abused" because we can rob 20 nearby stores without having some sort of cooldown in between robberies thus making the percentage of success in obtaining other materials besides money quite likely to give something else rather than the paper.
Else I would suggest after the robbery (where the worker is ducking with his hands over his head and in between his knees) you could search for a specific place Mike assigned to the business' characteristics to: search for weapons if they have those under the counter, safes that would take some time to crack-open, etc. — thus forcing the criminal staying inside the store he just robbed, receiving one more star, and police being notified in the chat that player is trying to bypass the safe's security at the same spot.
Neutral because you might be onto something creative.