@Seshi what a great topic!
For me, deciding to eat mostly fruits & veggies & cutting out fast foods have completely changed my food budget for the better. I'll give some examples:
I used to go to Subway at least 5 days a week but sometimes up to 7 days a week & I'd spend at least $10 everyday. Doing that 7 days a week meant that I was spending at least $280 a month and that's just for one meal each day! Now that I've cut that out along with all other fast food places & just make my meals at home, I spend less than $280 for all of my meals for the entire month.
For my breakfasts I have things like fruit smoothies made with thawed frozen fruit, some nonfat Greek yogurt, a dash of cinnamon, tumeric, & flaxseed, chia seed, or hemp seed, as well as things like avocado toast, egg white omelettes seasoned with herbs(I buy containers of just pure egg whites that are about $5 a 32 oz. container which will last me well over a week, so less than $1.00 a day plus it's a great source of protein & also happens to be fat free), cold cereals like Special K or overnight oats or hot cereal like regular oatmeal(oats & oatmeal tend to be very inexpensive & are also very filling), & also turkey bacon.
For lunches I sometimes either have salads or Lean Cuisines(these are often on sale at my local grocery stores & even when they aren't they are usually only $2.50 each. I don't eat more than 5 per week, if that, so I spend about $50 a month on them.) I also try to add in another smoothie to help keep me full & from snacking until dinner time.
For dinners I'll either have some lean meat i.e. chicken breast, tilapia, or salmon probably baked or broiled with some steamed veggies, pasta, or another salad. If I'm feeling really lazy, I'll just have a sandwich or Lean Pockets & call it good.
As for my smoothies, I buy a lot of frozen fruit. A 3lb. bag at my local grocery store costs about $8 & I get several bags because I mix the varieties & they last at least a month so I'd say I spend about $40 a month. For all my add ins i.e. nonfat Greek yogurt, skim milk, etc. I'll add another $35 just to be safe, so $75 a month for my smoothies, keeping in mind of course that I have my smoothies everyday & more often than not, multiple times a day.
The rest of my food budget gets spread out over things like lean meats, some processed foods, condiments & sauces, & fresh produce as well.
I'm on a weight loss journey, so I'm also doing this to improve my health. And yes, I know I mentioned quite a few fat free items but I do realize that some fat is needed for good health so I try to get that fat from the lean meats that I eat as well as things like avocados, nuts, & the different seeds that I use in my smoothies. And of course, I still have junk/snack foods occasionally but nearly as often as I used to.
Oh, which reminds me! Another reason I was able to cut down my food budget is by cutting out things like sodas & instead opting for brewing my own tea or drinking skim milk or water.