I keep seeing farmers selling stuff like apples, potatoes, etc on greenmarkets from large reusable plasic or wooden crates. If I bring my own bags, I produce no packaging waste.

It's a bit harder with things like milk, but should be doable using large multi-use cans and pouring into customer's bottle.

Likely packaging waste can be greatly reduced, if not eliminated completely, for things like bread, cookies / crackers / etc, eggs, sausages, butter, etc. Just use large reusable / recyclable containers, and parcel out the amounts needed for a customer.

It of course is not going to work well with stuff that requires special packaging at the point of production, like carbonated drinks.

The biggest problem is the lack if self-service in much if this; a salesperson should measure, weigh, cut or otherwise dispense things, and this is slower than scanning bar codes. Pre-packaged goods even allow self-checkout.