I once built a sailing canoe on Majuro Atoll, Republic of the Marshall Islands. I used Pandanus keys washed up on the beach as paintbrushes. Pandanus is a local fruit. After it's been bashed on shore for awhile the fibers at one end make a nice brush. I didn't have rubber gloves to use with the epoxy. So I figured out this nifty way to put a plastic disposable shopping bag on like a mitten and use it instead of a rubber glove.
I've been using this method ever since.

Excellent photos by theinfonaut The hand model is Bhaskar Mookerji a.k.a. "Buro".

Step 1: Place Hand in Bag and Wrap

This is the key step. If you start by pulling the bag to one side instead of the other the handle loop won't be long enough to loop over your thumb. You'll be off by half your wrist circumference.

Try it both ways til it works.

Step 2: Catch Bag Over Thumb

Wrap clockwise or counterclockwise, whichever you prefer.

Handle the bag somewhat carefully to avoid ripping it.
If you look carefully you'll see a hole by Buro's finger. That's because these shopping bags are all made wrong. As my dad would say, "It's not made for what it's designed for". The folded gussets at the bottom of the bag will rip two holes in the bottom of the bag if you actually use it to carry groceries or handle it roughly.
If you were to cut across the bottom of the bag and weld it together flat like a pillow case you'd have a much stronger bag that would carry more stuff and last longer.

Write your congressman and picket the grocery store demanding properly made bags.

Step 3: Fini!

Conduct battlefield surgery with confidence. You now have a plastic bag on your hand. All you need now is a sharp soup spoon, a bullet (for your patient to bite on), and a big bottle of whiskey (for you).