Next time you are at drive thru, pay for the next person's order. I have done this several times but one time in particular sticks out in my mind. One day I was at Starbucks and you can tell the lady behind me was having a bad day. Her car caught my attention when she pulled in behind me. Then she grabbed her bag in a jerky motion. I watched as she dug through it with exasperation. The body language from her passenger made it look like they had been arguing. The passenger was turned away. Then the woman dropped something between her door and seat and was digging for it. When the Starbucks person handed me my drink, I told i wanted to pay for the order for person behind me. She asked if I knew them and I said no, she just looked like she needed someone to do something nice for her. After paying I drove off. The way this particular Starbucks was set up I had to drive back past the drive thru to get out of the plaza. As I drove back by, she honked and she and her passenger were waving thank you. It seems to have brighten both of their day. Most time when you pay for someone like that you drive off and are gone before they even find out you paid.
I wrote this before I saw your post on your other question. Another thing you can do is have a $5- $10 gift card for a fast food place and when you see a homeless person you could give them that. If you have books you have read and no longer want, or even some clothes you no longer need but are in good shape, you can donate them to a shelter for abused women.