This backpack pattern is so simple to sew you can make one up in less than an hour.
I use to send my kids to swimming lessons with these backpacks as they were small enough to fit on their backs but large enough to hold their beach towels, brushes, bathing suits and other bits and pieces that they needed.
As I always made mine from cotton they were simple to throw in the wash (after removing the cords) to get rid of the chlorine smell from their wet bathing suits.
These can be used for all different purposes for kids, filled with what they need to go off to day camp, bible camp or off to friends for an afternoon.
Of course these are ideal for yourself during the summer when you want a fun bag instead of a purse.