Whenever I go someplace to eat, if I have cash on me, I pay the bill in cash along with tip. If I don't have enough cash on me, I pay the bill with my credit card (easy to keep track of my spending), but I will also leave a couple of bucks in cash as a tip. Kinda cool to watch a server think you stiffed them on the tip, and then be surprised when they get the tray back with a couple of bucks on it.
When I was in Amarillo, I had the same mail dude who always delivered to my house. Tex and I would stand on my porch and shoot the breeze on days when he wasn't rushed, and it was a pretty nice part of my day. And, whenever Thanksgiving or Christmas came around, my room mate and I ALWAYS made sure to give him a gift card of some kind (usually a restaurant card or VISA gift card). After awhile, he started bringing me small presents (dude even figured out my birthday, which was neat, never found out his though), and the gift exchange was a nice little tradition between me and him. Was really bummed out when he moved. Especially because then they started rotating mail carriers, so I never really got a chance to know the new ones.