You should definitely look into applying to a couple credit cards. Depending on your spending habits there's a lot of ways to earn a decent amount of rewards points/cash back. I have 7 credit cards that I used based solely on the type of purchase I'm making to maximize my rewards earning (but I've spent a lot of time researching and keeping track of my spending). Probably the most flexible options are any of Chase's cards (Freedom, freedom unlimited, Reserve and preferred). The 2 freedoms don't have yearly fees, but the others do (but those honestly pay for themselves easily). Amex and Citi have a couple flexible options as well. These types of cards are normally a lot better than getting a card from a specific retailer as the earnings are similar and you can use them for a lot more (cash back, flight/hotel awards/bookings, etc).
Also, if you apply for a new card make sure you spend enough to meet the sign on bonus as there's a lot of value to be had there. So if you know you'll be making a decent sized purchase you should consider applying for a new card right before.
Obviously you should stay away from credit cards if you feel you'd have difficulty paying off your balances on time, but otherwise you're leaving a lot on the table by not having some.