You dont have to buy anything extra...just use for things you have to spend monthly. Like your electric bill, water, gas, groceries, spotify, on-star... your not buying anything new, and you get your rewards.
I put everything on rewards cards. It also makes more sense safety wise to use credit cards on the internet and in public and never use your debit cards. If a credit card gets comprimised, use other cards until you get it straightened out. If your debit card gets compromised, they have to shut it down and send you another. .... very scary because that is where your money it. I even have 2 Credit Unions I use and keep money money in both..if one gets compromised, I still have access to money and life goes on.