It's also fun to use things like used toothbrushes and other brushes such as old make-up brushes or cleaning brushes to paint with. You can get scraps of paper from printers. They are called offcuts and are often available if you ask. You may be put on a waiting list. Buy the best paper you can afford and have lots of it.
Sketchbooks are also a great way for a child to keep their drawings all in one place.
I used to keep a pad of paper and a package of pens in the car so that my children could entertain themselves on errands. You may also want to include a roll of tape. If you keep something like this in the car, then your children have something to do when you get stuck in traffic or just on normal everyday errands. I made one for each child and kept them in the car. They were worth their weight in gold.