And when other people let you merge, don't forget the Thank You wave...
Also, offer to carry things for old people even if it slows your pace. Hold doors for people with packages rather than rushing through them. Wait a bit in the parking lot to walk in with a colleague who just pulled in.
Interesting how a lot of these "random acts of kindness" can boil down to "wait a couple of extra seconds so you can..." - people who are in a hurry tend to forget that time isn't money, it's time, and time spent on increasing the ambient niceness isn't wasted or even spent, it's banked! What goes around DOES come around!
Aside: The main reason I moved South from the New England area can be summarized in one exchange I had with a friend:
Me: Hi, Matt, how are you? Matt (not slowing): I can't answer, I have to go to the library. I remember being amazed that someone could be too busy to return a greeting (Fine! would have taken less time) but not too busy to complain about how busy he was. And what was worse - I didn't even react at the time, it seemed OK to me! It was only when thinking about it later that I realized that although I'd lived there nearly 6 years now, this was NOT my tribe.