I was reading Ken Kifer’s article on building your own panniers, and he had a good suggestion on a DIY front pack: the bottom half of a small office waste bin. You can get kits to adapt handlebar brackets to baskets, you would apply one of them. The benefits include it being rigid, being brightly colored, and waterproof. The challenge is that you need to improvise a lid, and you probably wouldn’t get the benefit of a map window on top. However, cutting up a clear 2L soda bottle might give you a map window, come to think of it.
But what would make a clever lid? Huh–the rotating flap of a kitchen waste bin of course [forehead+palm=thwap!]