There might be cheaper alternatives but I have one of these

http://www.amazon.com/Noteboard-Ltd-Pocket-Size-Erase-Board-NB35X15/dp/B00EAOJA4Y/ref=sr_1_1?ie=UTF8&qid=1464308917&sr=8-1&keywords=pocket+dry+erase+board

It's a fold up dry erase board with a grid on one side. It's great for student stuff and bringing dnd stuff with you where ever

These are kinda slick:

(http://www.amazon.com/The-Noteboard-Ltd-Pocket-Size-NB35X15/dp/B00EAOJA4Y)