But, since those opportunities can be a little rare, don't pass up opportunities to just be cool to other people.
Hold doors open; pick up things people drop; mind your own business; do a little more than expected of you. Whatever.
Once I was standing in line behind a guy, when he took his wallet out of his pocket and a baggie fell to the floor. I picked it up and handed it to him, saying "you might want this". He was so grateful. His honest gratitude made me feel wonderful.
A few weeks ago I held the door open for a woman coming out of the post office. Her arms were ridiculously full and I offered to open her car door for her, but she said she was OK. She was still trying to get in her car as I was coming out of the post office, and I noticed she had dropped a debit card. I picked it up and handed it to her and she was very grateful.
No, neither of those examples are anything big. But I like to do what I can, so I try to watch for opportunities. I hope it makes those I try to help feel at least half as good as it makes me feel. I know when people do something for me, it makes me feel really nice.
And, imagine that: No one was forcing me to help. It was anarchy in action!