Deciding how many credit cards to own is a difficult thing due to the fact that credit scores look at both how many credit cards you own (it's bad to have too many cards) as well as your total credit limit and how much you're using (a good thing if you pay your cards off regularly).
In order to keep my credit score maximized, I have kept the first credit card I ever owned, though I only use it often enough to keep the account open.
I also have a cash back credit card that I use for every purchase I possibly can. I use this to earn the cash back and pay the card off in full twice a month.
Finally, I own a Target card because you can save 5% off of each purchase. When you price match other stores and own a bonus 5%, you can't beat that.
Yes, credit cards are a bad thing, but they can help your credit score so they can be necessary in many cases. It's just important to use them wisely.