I am interested in weaving willow into craft and art. I am growing willow in my backyard and I was hoping to make a beautiful and cool backpack for carrying mushrooms and other wild edibles out of willow. Do you have any tips for weaving the willow, making an effective or comfortable backpack, or how to make designs into it while retaining it's retention and breathability?
What you describe sounds like a variation on a willow basket. There is a tutorial here: Weave A Willow Basket. Once you get the basic technique down, then you can start tinkering with adjusting the form into a backpack form.
Now, you mentioned you want a "comfortable" backpack, so that means that one side of the "basket" will have to fit the shape of your back. That can be tricky. The simplest serviceable backpack will have that side flat; so that suggests a variant of a square or rectangular basket, which in turn requires a different weave for the base than a circular basket. A circular basket has spokes that then curve up to form the uprights, but for a square or rectangle, the base is woven more like a mat or a potholder. If the items you want to carry have much weight to them, you will want the backpack to sit rather high, closer to your shoulders than to the small of your back. What size are you thinking of? More like a schoolchild's bookbag, or more like a trekker's frame pack? If the latter, you will find a waist strap indispensable. That and the shoulder straps may require a very different approach than the handle described in the tutorial, because of flexibility. You might want to consider a different material for those.