It's also really great for "multi-modal" luggage going from one mode of transportation to another. It's a big bag, but you get to carry it on the airplane because it's easy to wedge into whatever space is available. You can reach under the flap to get or stow things without undoing the flap. It's not great for long distance hiking because there's no hip strap and the weight sits kind of low, but it's super handy for everything else, especially dumpster diving for groceries. Sometimes I fold the flap over the bike's handlebars to use it as a front bag.
Years ago I made a bunch of these packs for the St.Cloud Girl Scouts. This one may look like it's 150 years old, but I made this one myself, and have carried it all over the world. Now it's worn and weathered with patches and tatters.