If you insist on including fresh fruits and vegetables in your diet, then it's more realistic to take a trip once a week. If you can live on a mix of fresh and frozen or canned foods, try twice a month. Above all, the most effective way to stick to a grocery shopping program two or three times a month is to plan. You can save a significant amount of time and energy if you determine the most efficient way to go around the store to complete your shopping list.
Without knowing how much money you have available to buy food per month, it's impossible to create a shopping list and meal plan in the first place. I tried to do grocery delivery after receiving a gift certificate, and I was determined to make those foods last as long as possible. If you're trying to reduce your grocery budget, you might want to start lengthening the time between shopping and focusing on meal planning and looking for sales brochures.