Best thing for my diverticulitis is a low residue diet, no salad, no onion, no green leaf veg, no potato skins, no brown bread, pasta or rice, no wheat based cereal or oats, or muesli, no beef or pork or lamb, no peas, sweetcorn, baked beans, no digestives, or oat based biscuits. No berries or citrus fruits, seeds or nuts, no dried fruits, basically anything that's hard to break down.
I now have white bread but no more than two slices a day, eggs, white pasta, white rice, noodles, potatoes, well cooked carrot swede parsip broccoli cauliflower, chicken or turkey, shortbread, custard creams, wafer biscuits, banana, cooked apple not raw, plums but peeled not the skin, yogurts, mousses, custard, Rice Krispies, It's very limiting, especially when out, but it's the only thing that works for me in keeping flare ups at bay.