I used muslin. It really doesn't add bulk. I work on a couple at a time.
When I was doing crumb blocks, I'd get them big enough, then square them up and then use the leftovers for the next group.
They are fun and fast. I did the strip twist from www.quiltville.com and it was fun to see it transform the more colors were added. my pic is on the other thread of our projects for this year.