Leave your change in the soda machine for the next person. It's a nice surprise. Buy coffee for the person standing behind you in line. Tape a quarter to a pay phone with a note welcoming anyone who needs it to use it. Adopt a family through a social service agency, not just at Christmas.
People go hungry all year.
Plant a tree or some flowers for a local church. Perhaps offer to build a Memorial Garden. Volunteer at a local shelter, crisis nursery or soup kitchen. This will give more to you than you can imagine. Volunteer to read to children at your nearest library.