I've been using denim bags I made for about 20 years. I guess I was ahead of the curve here. I think I essentially made the pattern up from a regular grocery bag - similar measurements. Very heavy handles, never had a problem. They don't need to be washed often, if something is spilled on one I throw them it in with the regular wash.
I think today I would follow what others have suggested and just buy a bag and make a pattern from it. I wonder how many plastic bags I've kept out of the ocean in 20 years.