I didn't want the reward, but...
I work at a super popular fast-food restaurant in California. I serve hundreds of people a day, and I honestly couldn't even remember a third of their faces if you put them all in a room and told me to point out who's who. They come by, flash a smile, take their order receipt, walk away, and boom! Their faces are forgotten.
But there's always this homeless man standing in front of the store, trying to catch sleep before the nightly rush. People walk by without even glancing at him. One day, I saw him sitting there against the wall and I couldn't take it anymore. I quickly ran to my manager, asked him if I could take my 10-min break right then, and with his approval I ran back to the register and put in an order for a burger, fries and a drink. Then, once the food was ready, I walked out to the homeless man and handed him the food. He smiled, beyond words, and I walked on clouds back inside.
After my ten-minute break, my manager told me I was getting a raise and a promotion.
Don't expect a reward. But always do things for other people because you NEVER know what they're going through.