First of all, if you fly with one particular airline, consider becoming a member of their frequent flyer program. The loyalty programs are usually free and they allow earning miles on flights.
As for a credit card, you can apply for a credit card with rewards program. Most cards will allow you to redeem rewards for cash which you can use for anything you want. The cards will also allow you to improve your credit, provided you keep all your credit accounts in good standing, and later you will be able to qualify for an airline credit card like the one offered by United Airlines.