I love farmer's markets; I think they're great. Not only do they allow us to bypass the middlemen and get our produce directly from its suppliers, they also allow us to reduce our waste by reusing items even before we get to the third R of recycling. In these days of commercially produced disposable packaging, it's a bit of a foreign concept to take containers back to the seller, but I assure you that there are many opportunities at the Guelph farmer's market.
For starters, you egg-eaters out there can buy free-range eggs at the market, and keep reusing your egg carton. When you get eggs elsewhere, save your cartons and take them back to the farmer''s market vendors, who are always very welcoming and accepting of such donations.
Other vendors that will take your used containers back include the people who sell vegetables in baskets. If you have a basket from somewhere else, they are quite willing to take it off your hands. I even returned a larger one once, and they were somewhat excited that I had managed to procure a less commonly used size.
The cider places can't take your jug back, but are more than happy to allow you to reuse it. You can fill it up with your choice of "leaded or unleaded", meaning pasteurized or organic, for those readers who are as confused by the metaphor as I was.
Although I haven't had a chance to try it out in Guelph, I know that the maple syrup vendors in other locations are also happy to see their bottles coming back for reuse as well. In this case, the glass ones are better for returns, as they can be properly sterilized for reuse.