Nature Explorer Bag from Chez Beeper Bebe, but I've been procrastinating on figuring out the details of that pattern since I saw it. Still, it must have been bouncing around in my brain somewhere, because when I needed a way to recycle my favorite cargo pants, inspiration struck. Today I made these bags for my kids. They're pretty simple. Each bag requires half a pair of cargo pants, less than half a yard of fabric (for lining), about a yard or so of strapping, and some sort of clasp (I used overall buckles, which was convenient since there were two in the package, and they were pretty cheap for clasps).
Turn the pant leg upside down and lay it flat- the hem of the leg will be the opening of your bag. From the bottom of the leg (previously the top) cut a notch on each side, through both layers of fabric. the notch should be 1" wide and 1.5" tall (it's hard to see the black fabric in my picture, but you can get an idea of the shape from the yellow lining.
Then, fold your lining fabric in half and place the leg on top of it. Cut a similar shape (two layers), except 1/2" larger on the top edge and on each long side edge. The notches and bottom edge will be exactly the same.
Hand- or machine-sew the cargo pocket to the front of the pant leg, just above the notches (hard to see in my picture, but I promise it's there). Hand- or machine-sew the back pocket to the right side of one of the lining pieces, in a similar place or in the middle of the piece - just remember that the top of each piece will be creating a flap, so leave enough room for that. This will be a "secret" inside pocket.
I've sewn two of these things now, but if I were to make another I think I would increase the flap length - which would mean keeping the front pocket low, the inner pocket medium low, and the straps attached lower than they are shown here.