A bag of course!
This one was super quick to whip up,
and can be made any size you want.
I just put two pieces of fabric together,
right sides facing each other,
pinned the straps inside,
sewed around the outside leaving a little hole,
flipped it right side out and sewed up the sides.
I added a closure and two lines of stitches at the top for fun.
Jo put her books in hers.