Just beat the game !
Overall a very fun and well executed game on all aspects, well polished and the music really fit the game nicely.
As an idea regarding the player's challenge:
Maybe it would have been good to have an unlimited amount of ingredients instead, as sometimes I was hit by the dreaded salad and tomato only sandwich a few times in a row and ran out of ingredients, which felt a bit beyond my control as I could not possibly adapt to that.
For example some kind of timer to make the sandwich combined with a customer satisfaction bar that would serve as your "hp", and maybe some money tip bonus which would reward the player if you were really fast at doing the sandwiches so basically it'd add a "skill" element to the game.