Nakasero Market occupies a hillside in central Kampala and is where much of the city's food supply passes through. It is large, chaotic, and worth at least a wander. The produce stalls sell pineapples, passion fruit, jackfruit, plantain, avocado, and the full range of Ugandan vegetables. The spice section is good. Small stalls around the edges serve rolex, mandazi (fried dough), and simple cooked food.
Unlike Owino Market, Nakasero is primarily a food market, which makes navigation easier and the atmosphere slightly calmer. If you want to cook (or just want to understand what Ugandans eat), this is where to come. Bring small bills; vendors rarely have change for large notes.