Nancy, I only know of tutorials for all-fabric walker bags. But you would think that making them with pockets of granny squares would work and be cute. These 2 have the best photos and explanation of any I know.
This one uses four buttons, so takes button-hole making
http://www.laurassewingstudio.com/Sewin ... r_bag.html
This one is very sensible, firm and sturdy - better for a man, maybe
http://www.instructables.com/id/SewUsef ... nal-Touch/
Whoops - wait, here's one that's all crochet, but not Granny Square
http://www.myrecycledbags.com/2007/10/2 ... -tote-bag/
also read that using cotton yarn keeps it from stretching out if heavy things are carried, and that it is the pattern Veterans Hospitals give out for crochet donations.