30 minutes is on the longer side, but I think part of the point of walkable grocery runs is that you don't buy a week's worth of food like you do in a car. When I lived in Paris, I'd happily pop out to buy whatever I needed for a single meal. I had so many grocery stores within a 5-minute walk. Now that I'm in SF, I buy for the week (on my bike with panier bags) because the grocery stores I like are far from my home.