While I was in IL, my mother-in-law gave me several yards of chalkboard fabric. This is the coolest stuff -- it's vinyl, but can be written on and erased just like a chalkboard.
Modifying the crayon roll design by adding a rounded rectangle applique, we created this chalkboard roll:
I had no idea how tightly this would roll up, so instead of putting a ribbon w/velcro closure, I tried using a ponytail holder, not only to hold the chalk, but to wrap around it when closed:
It turned out ok, but there are some kinks that need to be worked out.
* Each ponytail holder needs to be stitched on top of itself instead of side by side (the chalk twists perpendicular to the roll).
* The chalkboard fabric was rolled the opposite way on the bolt, so the mat resists being rolled (actually I "folded" it). Only time will tell if the material will flatten out and decide to cooperate.