This game is so good, who thought a burger flipping sim would be so intense! Impatient customers, uncooked meat (oops) and zombies, all in the space of a five-minute ride? Amazing stuff!
Honestly, this concept is so simple yet executed so well, I think it would be awesome to have a level-based system where you have to meet certain achievements to pass (feed 5 people, kill 5 zombies, no more than 5 casualties and so on). Don't know if you were looking to expand upon the initial idea but I'd definitely invest a lot of time into a more fleshed-out (or rotten, diseased and dying fleshed-out) version!
Whatever you decide to do going forward, keep up the awesome work, this was a blast =)