How bad would it be of me to quit this job?

I work for a small pizza place as a delivery driver. I was hired for very part time hours, working short shifts in the evening.

I found out that my manager is taking a vacation for two weeks, and has given me 10-12 hour shifts to cover for him while he's away. I am not very happy about this, because long hours like that are very intense for me, it's been a while since I have been working and this job was intended to be something small I can work for some extra money until I can get into something better. It's a minimum wage job, but I get to keep tips. I'm really not making any money due to how expensive gas is right now, and I have never been able to do more than 5-6 deliveries in a shift, which is normally a weekend.

So, how bad would it be of me if I were to just not show up? I kinda hate that I am even asking, but I've been thinking this over for the past week, and wanted some opinions just to see what the general consensus is.