Never hurts to sign up for a carrier's frequent flyer program. United, as an example, has miles that don't expire, so if you fly coast to coast once a year, that's 5,000 miles. Some other programs may have miles that expire without some account activity every 18-24 months, so if you credit elsewhere just keep an eye on that. You don't need to fly to keep frequent flyer accounts alive by flying - all sorts of partner activity will qualify from dining to airline mall purchases.

Airlines typically offer their own branded credit card for less than $100 a year. Alaska, as an example, and something that is unique to them, offers a companion ticket each year with their credit card. For $99 plus taxes, a companion can fly with you. Airline credit cards may offer things like free checked bag or seat selection, in addition to bonus miles for signing up. I just signed up for a United credit card that came with a $250 credit plus 25,000 miles - one that was hard to resist even though I don't fly United a lot. Once you settle on an airline that you might want to fly each year, you might find a credit card that's worth having at least the first year for the signup bonus which might be enough to cover a free trip on domestic routes. You can always switch to a cash back card later. I have a 2% cash back card but it only came with a $100 signup bonus, worth a lot less than what's out there for airline credit cards.