Once a month seems like a very long cycle. I buy groceries and other commonly needed items 2-4 times per week. Of course, I live within walking/biking distance of several stores, and I hardly ever buy more than what I can fit in a bag.
Still, only once per month seems very little, especially for perishables.
Once a month seems extremely low. We do one big shop a week, and that's with a lot of planning(we do a massive shop for all dinners and lunches for the entire week) and that's with using long-life milk and freezing bread so that we don't have to go to a shop more often.
Still, only once per month seems very little, especially for perishables.