LevelUp is a free smartphone app that lets you pay with your credit card using just your phone. Not only is that super convenient, but you also will get $5 free dollars if you sign up with my promo code, you'll earn me $5, AND most companies give you a few free dollars the first time you use LevelUp with them, AND every $50 you spend at a place, you get another five free dollars there (or sometimes it's $100 and then $20 or $50 and $3 - The companies choose their own rates). It's especially awesome for those of us who like to go to new places all the time. I can't tell you the number of places I've been to and gotten food or a drink for free or like $.20 'cause I use LevelUp.
A list of my LevelUp-participating reviews thus far: