Maxpedition make some great durable bags, their latest addition is the Xantha Internal Frame Pack,
an ultra durable backpack built to resist the elements. The backpack is
a comfortable pack for day use and rugged 3 day trips, it features an
internal sheet frame with aluminum stay for additional support when
carrying heavier loads, a pouch for a 100oz hydration bladder, drinking
tube ports, several mesh pockets, and handy pouches for keeping small
items close at hand. It also includes a padded removable waist belt to
help distribute the load. Available in various color and textile
options.