Recycled Map Waterproof Pencil Case
First I cut some plastic to size, the non adhesive type ( $1.50 from Office works) and used double sided clear tape to hold the paper in place.
The plastic is on the inside and outside and I cut a separate lid from paper but it was one piece of plastic on the backside, if that makes sense.
The sewing machine was then used to sew along the top front panel, then zig zag all around the sides, bottom and top.
The flap folds over if you crease it and leave something heavy on top for a few minutes.
Any recycled paper could be used, or colouring in sheets, books, photos, any size and it is fairly waterproof, although I haven't poured water in it!
I think a long skinny one would be kind of useful and you could put velcro on it to keep it closed and make sure your pencils didn't fall out.
Total cost, less than 50c, if that.