I love this!
Acknowledge homeless people, even when you don't have (or don't want to give) money. I look them in the eye, say hello, answer any question (normally, can I give them money) and wish them a good day just as I would anyone else who I meet in the street who asks me something.
Dance to street performers' music.
Bring reusable bags to the grocery store and other shopping trips. Whenever possible, avoid using extra packaging and bags.
If you must buy new clothes or shoes, buy from companies and that are socially and environmentally responsible. It's normally really expensive, but that is because they aren't paying their labor $0.05 per hour or polluting the heck out of everything. And we don't need as many clothes as we think we do anyway. The bonus is that normally you get a superior garment that is well-made and has fewer chemicals in it.
Look for farmer's markets, co-ops, and CSA farms.
Turn off lights in rooms you aren't in and unplug appliances you aren't using whenever possible. Many appliances use around 40% of the energy if they are plugged in but off.
When people sit next to you at an airport, on the bus, where ever and want to talk, talk with them. Maybe it's just me, but I have random people tell me all about their problems on a fairly regular basis. They just seem to need someone to listen and be sympathetic.