I love the picking up trash idea, and the suggestions to bring in the paper for the neighbors or deliver cards to nursing homes are great, too!
Does the school have a paper recycling bin? (Ours does - it's a dumpster, painted bright green and yellow, and it's just for paper - all sorts - and the recycling company pays the school by the pound, so by putting our paper in it, we are both recycling AND donating to the school. Bonus for us, since the only paper our neighborhood recycling company takes is newspaper.) Maybe his household job could be making sure paper goes in a special bin to be dropped off once a month or so? (We have an old printer paper box in the garage, for empty boxes and newspapers, and other "clean" paper stuff. We dump it into the bin, and re-use the box, but the box is cardboard, so if we drop it by accident, it's recyclable, too.)
Tape quarters to the vending machines in hospital waiting areas?
Call the food bank - they don't all let kids help, but some will allow the younger kids to sort cans for them. That's a single-afternoon time commitment.
I don't know how it is there, but here, wildflower season is coming up - probably not as much a draw for your son, as it is my girls - is there a place he can pick some to surprise somebody? You can usually find little vases at craft stores or the dollar store.
Good deeds don't have to be just people, either. Have him maintain a bird feeder. Or collect old linens or clothes for the animal shelter - they'll take anything, as bedding for animal crates. Even if they are in very bad shape - they will use them for sick or unvaccinated animals, so they can throw it away and not spread germs. Bonus: a lot of time, shelters need help socializing and exercising animals. So call the shelter first, but he would probably be allowed to walk smaller dogs or pet the cats and rabbits while you are there to drop things off.