To clarify for anyone unfamiliar with these deals, you can already get a 5% discount at Target with their debit card, which doesn't require a credit check, as it just links to your existing checking account. Also, the Chase cards I mentioned dont have annual fees, and the Flex has rotating 5% cashback categories each quarter (gas stations, Walmart, Amazon, utilities, etc.), as well as 1% back on everything.
There is a whole community of people who "churn" credit card offers/perks, and it's crazy how many cards some of them go through. If your credit is good, and if you can refrain from overspending, you can get some nice returns. I opened 3 credit cards about 7 months ago, and made around $1200 with sign up bonuses, plus I continue to make money with their cashback rewards. My credit score took a slight hit, but it's now back up to where it was before I opened them (790'ish).
Checking/savings account bonuses are even better, because they rarely impact your credit score, and are easier to qualify for. Swagbucks/Mypoints often run promotions, and sometimes they stack with the bank's offer. I do these quite often, and generally look for them to be at least $100 to open. Most require a payroll direct depost for 1-3 months, but some just require a single cash deposit. Off the top of my head, an easy one right now is the Fidelity bonus that has no credit check, no fees, and pays $100 for a single $50 cash deposit.
The website "Doctor of Credit" is a great resource for these deals, and they keep track of the best credit card/checking bonuses... they also have a very active and helpful community.
Of course, do your own homework on any deals like this, and dont take on credit cards unless you can control your spending.