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
Try it both ways til it works.
Step 2: Catch bag over thumb
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.