If you shop at open-air markets, you can save on food and other perishable goods (like flowers and plants) if you do your shopping during the last hour before the sellers go.
Since the sellers cannot keep those goods, as the next day they are likely to be rotten, they’ll sell them cheap. The downside is that you may not find a big choice as you’d find in the morning when they start but, after a couple of visits to some street markets, you’ll learn when it’s the best time to find your favourite items and what you can find easily. Another good aspect of shopping late is that there are less people and you don't have to queue.
Buying at open air markets is also a good way to support local traders. Now more and more there are local farmers markets, with locally grown fruit and vegetables, honey, bread and dairy products, poultry, organic products.
This means also better food quality, less environmental impact (due to transport, industrial farming), which will save us a lot in terms of health.
You can get to know the producer, learn about how they produce their food, get recipes, advice. I think, generally, buying at street markets is a nicer experience than buying at supermarkets: you take a walk, get some fresh air, markets are colorful, you may meet someone you know, have a chat and find something totally unexpected.
So, I encourage you to visit your local markets.