I love this idea and wish I'd thought about it when I was in high school.  In fact, I've been trying to think of how to start an art group for adults in my neighborhood, so I might steal some of the great ideas posted here.  If you are thinking about using craft to do some good, there are some really simple, green, fun projects that you could do in a volunteer setting with children or the elderly:

Egg-carton flowers:  Cut up the individual egg cups from a washed egg carton, the foam ones work best.  Punch a hole in the bottom of each cup.  String a pipe cleaner through the hole, and decorate the egg cup to look like a flower using paint, Sharpee markers, stickers, glitter, fabric, ribbon, or whatever else your heart desires.  You can enlist people of all ages and abilities to help decorate.  The individual flowers are lovely or you can put a few in a boquet for a real creative pop! You can also "plant" these flowers in a home-made pot.

Blooming Seed Planter:  Take an empty can (the large ones for canned tomatoes or pumpkin work best), remove the label and the top lid completely.  Punch holes in the bottom lid.  Decorate the outside of the can using Sharpee markers, stickers, foam cutouts, etc.  Fill the can with potting soil or compost.  Plant seeds in the soil and water.  Take foam egg cartons.  Cut out each egg segment into individual cups.  Color each cup to look like a flower.  Punch a hole in the bottom of the cup.  String a pipe cleaner through the hole to make a stem.  Bunch together the completed egg carton flowers and wrap around the top of the can.  Alternatively, you can push them into the soil so they look like they are growing, just be careful not to put them on top of the seeds.  Place the can in a sunny window or outside on your porch.  Water regularly and watch the real plants grow!

Bird Feeder:  Take an empty plastic bottle with a handle (large vinegar or milk bottles work best), remove the label and cut a large hole or window in the side opposite the handle. Decorate the outside of the bottle using Sharpee markers, stickers, foam cutouts, etc.  Use heavy wire or a wire clothes hanger to form a hook around the handle. Fill with bird seed and hang outside in a tree.  Watch the birds gather.

I love egg-carton flowers.  Cut up the individual egg cups from a washed egg carton, the foam ones work best.  Punch a hole in the bottom of each cup.  String a pipe cleaner through the hole, and decorate the egg cup to look like a flower using paint, Sharpee markers, stickers, glitter, fabric, ribbon, or whatever else your heart desires.  You can enlist people of all ages and abilities to help decorate.  The individual flowers are lovely or you can put a few in a boquet for a real creative pop!

Last spring I worked at a community fair and hosted a little gardening craft booth.  The two projects I introduced were really cute and did not require a great deal of ability, but could also encourage those with lots of inspiration to go to great heights.  These were also fun projects because they reused/recycled items.

Project #1--Bird Feeder

Take an empty plastic bottle with a handle (large vinegar or milk bottles work best), remove the label and cut a large hole or window in the side opposite the handle. Decorate the outside of the bottle using Sharpee markers, stickers, foam cutouts, etc.  Use heavy wire or a wire clothes hanger to form a hook around the handle. Fill with bird seed and hang outside in a tree.  Watch the birds gather.

Project #2--Blooming Seed Planter

Take an empty can (the large ones for canned tomatoes or pumpkin work best), remove the label and the top lid completely.  Punch holes in the bottom lid.  Decorate the outside of the can using Sharpee markers, stickers, foam cutouts, etc.  Fill the can with potting soil or compost.  Plant seeds in the soil and water.  Take foam egg cartons.  Cut out each egg segment into individual cups.  Color each cup to look like a flower.  Punch a hole in the bottom of the cup.  String a pipe cleaner through the hole to make a stem.  Bunch together the completed egg carton flowers and wrap around the top of the can.  Alternatively, you can push them into the soil so they look like they are growing, just be careful not to put them on top of the seeds.  Place the can in a sunny window or outside on your porch.  Water regularly and watch the real plants grow!