Cheap/Free fun crafts or art projects for kids 3-12?

The kids want to have an arts and crafts day tomorrow, but we’re on a tight budget this week and I have no intentions of going out to buy a bunch of supplies. The kids range from ages 3 to 12, so I need projects that will be easy enough for 3 and 4 year olds (with assistance) but not boring or too simple for the older kids.
We have a lot of stuff around the house already, as far as supplies go. Tons of paints, play-doh, paper, construction paper, stickers, crayons, coloured pencils, glue and glue sticks. I also have a bunch of sewing stuff like fabric scraps, buttons, trim and string. I have one empty paper towel roll, and I think I have one empty toilet paper roll.

Any creative ideas from the collective?