Here's a simple, no-sew, tote-style shopping bag made using only some found plastic sheeting (in this case: billboard material) and duct tape (multicolor, of course)
Step 1: Prep Found Material
I modeled this after a canvas tote I use all the time, which results in a square bag. In this case, I used an 18"-square, so begin by measuring out 36"x18." Choose which side is in/out (photo shows inside).
Step 2: Make Flat Bag
I lay down the tape on both sides then flipped it to fold/seal.
I folded down the top inch or so to give it a nice clean look. Then, lay down a border of tape.
Step 3: Create Bottom to Shape Bag
Reach inside the bag and flatten out a bottom, in this case a 6"-wide section. Allow the corners to fall inward and crease (not unlike gift-wrapping).
I added a line of tape between the two corners to keep them place and reinforce the bottom.
Step 4: Finish Seams
Turn right-side out (in this case, the printed graphic).
Reinforce seam and bottom with continuous line of tape, if desired. I liked the bright accent color.
Step 5: Add Tape Straps
Instead of using more plastic, I tried making 1" straps by folding duct tape on itself.
Accidentally, I halved the length, which created an opportunity to add another and alternate colors, which I attached using the matching accent color.
Finally, I lay down another thick border of tape over the straps along the inside to attach.
Step 6: Ready to Shop!
It's ready to use immediately. I tested it with some random heavy things in the studio. Then, wondered if it was waterproof (love duct tape!), so put about a gallon of water inside, and literally swung it around to see if handles would hold. Of course they did: it's duct tape, and it held water very well. Some tiny tears in the plastic leaked, but not the seams.