Here's a life hack for you.

If you're ever in need of a whiteboard for drawing/sketching, grab a few white a4 paper sheets, a roll of transparent duct tape, tape both sheets together side-by-side. Cover both sheets with tape

et voila! You have yourself a portable & foldable whiteboard!
The more sheets you involve, the bigger the whiteboard will be :)

P.S. It's very handy!!