Some days I try to come up with an actual activity with them. Some of the things we have tried are:
Perler beads (fusion beads)---these are a great craft to help with fine motor skills. They also encourage the development of patterns and can help children with counting and colors. The girls and I really enjoy the perler beads. It's amazing the amount of time that the beads can fill when you are looking for some quiet creative art time. I usually use my Michael's 40% off coupons to purchase the beads and just the other day I got a huge bin of them at IKEA for $5.99.
Craft kits---I also like finding various craft kits already assembled. We've bought kits for door hangers, frames, mirrors...you name it. These are easy and inexpensive.
Fabric Crayons---For years I have been using Crayola fabric crayons with kids. You create a fun design/word and print it in flipped mode. Then the kids color the design with the fabric crayons. Tip for the use of the crayons-be sure to press down hard when using them for the best effect. Then iron the design on to the Hanes $1 t-shirt from the Dollar Tree for a fun new summer top that's unique to your child.
Scrapbooks---This summer I am putting my MANY scrapbooking items to good use. At Target I purchased a pack of photo albums. The larger album holds 4--4x6 photos on each page. I have been printing out pictures from our summer activities and then I arrange them in the album...usually 2 or 3 per double page. The girls then decorate the 4x6 card inserts with information about the photos and various scrapbooking items. It's a fun way to document their summer, as well as, learn some scrapbooking techniques in an organized fashion.
Finally, I am following this fun site for more ideas in the world of art. Love the variety of art supplies she uses to create fun projects.