In other episodes people say that Jack and Rebecca have only known each other for a week before they go to L.A. When they meet he only had 9 bucks, and is unemployed so it seems odd that a week later he has enough money to pay for hotels, food and gas to get to L.A and back.
However, he could have had some saved money still left that he didn't gamble and lose due to being robbed. His mom could have had savings, and he could lend from her and/or her friend. He also was repairing cars of people he knew and asking them to recommend him to their friends, so he could have earned some money that way, too.