I always have cash on me. I have never linked my credit card to my KTTW. I personally find that I can better keep track of my spending if using cash than if I charge everything to my key.
So that I don't overspend, I usually have a set amount that I carry with me everyday (about $70-100) for tips, beverages if its super hot (I don't like to use my snack credits on water or juice/soda), souvenirs I want to purchase.