A plastic canvas product (with small holes) comes in sheets and it’s what I plan to put in the bag bottom. I will tack it in the corners to hold it in place.

I would want to make sure the upholstery fabric is washable. Bags can get dirty and bacteria laden so you need to wash them on a regular basis. I have some of the fabric ones from the grocery store and some I made out of canvas. About once a month I throw them all in the washing machine with the regular laundry. If I ever think I got something easily contaminated on them (meat juices or broken egg for example), they go in the wash right away.

There were two problems I had with my own "handmade" bags: 1. they would not stand up and open for me or the cashier to put groceries in them. Kept flopping over. When I tried re-inforcing them to be more sturdy, the weight became a problem. and #2 the first ones I made the handles were too short: an easy fix by making the handles long enough to fit over the shoulder, made much easier to carry multiple bags. I basically solved both problems by just buying the heavier plastic type ones the grocery store sells, usually about 99 cents. They last a long time and if you put your meats in a regular plastic bag, they stay pretty clean.
I would suggest making only one or two to try out before you make a stack of them, that way you can see if they will work for you and if you need to make any adjustments before you have spent a lot of time and effort in making a bunch them.
Every grocery store has its own unique bagging system, some more "friendly" to the "green way" of bagging than others.

I purchased all mine from WalMart for less than $1. I have had most of them for years. They have held up so well that the cashiers always think I am just now purchasing them. The have the fruits and vegetables on the outside. WalMarts original blue ones did not hold up well; but the newer one are great and I would not cut out and sew a bag if I could purchase one for $1.

How great that you're town is going plastic free! I wish it was never invented, same with styrofoam.

I use empty cat food bags. Open bottom and clean them, sew the bottom and box it, and add handles in a little hem around top. Really strong.

I have made a few out of dry dog & cat food bags, and dd has a horse, so those feed bags are good too..as mentioned above, a bit of sewing and there's a grocery bag!..I keep them in back of vehicles. Also keep a styrofoam cooler back there, pop in one of those freezer keepers....for ice cream, milk products, if I'm planning a list of errands on that day

I'm going to make some new shopping bags from heavy muslin or canvas and the bags I get from buying bird seed. The bird seed bags are such a great heavy duty plastic with pretty scenery and colors. I've been saving them for about a year now. Should have more than enough for what I want to make.

I wish I had a pattern but I like the bags that fold into a small pocket. It is made of the poly used for light weight wind breakers. It has held up very well. A friend made one out of cotton and the pocket was heart shaped. It hasn't held up as well though. But no pattern sorry. Maybe do search.
Lynda

i have chicken feed bags and dog food bags and kitty bag and i have made a lot of bags for me
and my sister and my cousin. we take them to sams club twice a year and we are surprised how
much stuff they hold and are very heavy duty. i just google making bags out of feed bags and
follow that pattern they work great