Markets on the drive from Paris to Burgundy?

Usually these markets are a weekly thing, not daily. In Vezelay itself for instance, the market is held every Wednesday morning. So before anyone can give you meaningful advice, we would need to know on what day of the week you plan to make this trip.
Another option of course is to stop at one of the large supermarkets.

There is an Intermarche in Nemours just off A6 if you are looking for a supermarket.

On the A6, take exit 19 (Auxerre) , just after the exit you will find a first commercial area with 3 (low-cost) supermarkets: Cora, Lidl and Aldi
All 3 open every day and Sunday morning.

Continue for approximately 2 miles on the Nationale road N6 towards Auxerre and take the right line direction: Perrigny.
you will find a "Grand Frais" supermarket with better quality products, also open every day and Sunday morning.
Personally this is where I would go.

https://maps.app.goo.gl/TZjdr3AXHGf5VZXB6

Thanks so much for the information! Yes, I generally meant supermarket, but I didn't want to rule out smaller, family-run groceries (perhaps I should have used that word) if they were worth the trip. Truly appreciate your help.

Many of the small family grocery stores have gradually disappeared since the 80s and have been replaced by suburban supermarkets.
Now these supermarkets buy the premises of small family grocery stores in town that have closed and open local branches like Carrefour with the small Carrefour Market stores.

The best way to find these family businesses is to go to the market in the morning

Thanks so much JoLui. We plan to stop at the Grand Frais in Perrigny. Unfortunately, this is much-too-short trip for a family occasion so we may not have a chance to visit a market. But I will look into it!

I greatly appreciate everyone's input.

And I'm sorry to hear about the small family-run markets. I remember them fondly from my last trip to France, which was way back in the 1980s!

It seems that you would like to at least walk through a farmers market. There is an excellent one in Chablis on Sunday mornings, exit Auxerre North of the autoroute, 14 kilometre distance, direction Tonnerre.

Merci beaucoup! Yes -- we would. I will try to learn more about this market and appreciate the recommendation. :-)

So many very kind and helpful people on this forum. Thanks to you all.

Not sure if it's kosher to ask this here (rather than start a new topic) but we'll be returning to Paris on the last Sunday of August, which I understand will undoubtedly mean heavy traffic.

What time of the day is best for a bit less traffic? We won't be able to leave before 3 p.m., as we have a family commitment. I'm wondering if driving to Paris in the late evening means heavier or lighter traffic.

Merci encore!

Any Sunday is bad but the last Sunday of August is the worst. Drive back as late in the evening as possible or at night.

Thank you for your reply, Bets!

Depending on your Paris destination, on a high-traffic day it can be faster to take the A19 and A5 to Paris than the A6 all the way. Especially for the eastern half of Paris.
Also, on such days traffic is often very dense on the 2-lane section of the A6 south of Auxerre, so coming from Vézelay you might as well drive to Auxerre than try to join the motorway at Nitry.

Thanks, Balso.

Much appreciated!

Just search for "Carrefour" on Google maps and you'll find the only chain I know that's in small towns and open even on Sundays (sometimes).

Danke schön, KGC. :)