Nice things you do for no one in particular.
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Every time I leave a store that has someone ringing a bell for the salvation army, I give at least $2.
I sometimes will take shopping carts that people don't return to the cart return place.
Leave anonymous love notes in peoples tip cups.
No really. I have paid for and dropped candy/mints/treats in people's trunks at the grocery store.

I rarely park in the closest spots to a store in case there is a senior citizen or someone else who has problems walking.