This past Christmas I made a waterproof lined wash bag for my nephew James to match his duffel bag and pencil case that he can take on holiday and when he visits his grandparents. To keep the washbag practical I lined it in a waterproof lining and for ease of use I made the drawstring channel nice and wide so he could easily open and close it.
Here's my Waterproof Lined Drawstring Wash Bag Sewing Tutorial...