Instead of buiding Colesworth-style supermarkets and competing with their duopoly, they could focus on warehousing shelf-stable, non-perishable essential items:

• UHT Milk (dairy and otherwise)
• Bulk bags of pasta, dry grains and legumes
• Flour, sugar, cocoa and similar basic baking supplies
• Cordial/Juice/etc
• Cookies/Biscuits/Crackers
• Nuts and seeds
• Canned/Jarred/Dried veg and fruit
• Toilet paper etc

That way they don’t have to worry about refrigeration or freezing in their supply chain and can just store things. They can set up shop anywhere not having to build a massive building with cold rooms and elaborate air conditioning like regular supermarkets.