Question about rebuilding new credit?

I've got a credit score of 600....about 3k debt (my car is the majority of that, almost paid off) and have a steady job with good income. I've had multiple small loans paid off in good standing over the years but with companys that don't report to the credit bureau (small loans) and I really need to start building new credit that actually shows up when paid. I know I can't qualify for a credit card due to my FICO but what about a gas card? It can sure help with gas right now since I travel 100 miles round trip to work. I can pay the card off every month easy. What do you think? What is a good gas card?