First, learn to cook. I don’t mean to sound flippant, but once you know the basics then you can start expanding your skills and buying food means buying ingredients rather than something already made, processed, and packaged. Ingredients are almost always cheaper. Once you have this foundation then you can go to the kitchen and whip up a quick dinner rather than taking the easy but expensive way out and driving to the nearest drive-thru. $20 per day on fast food is $600 per month, $25 is $750 per month. That’s an insane amount of money spent to feed one person.
Look for cheap ingredients. Buy store-brand stuff. Yes $5 can of Cento San Marzano tomatoes will taste a bit better than a $0.75 can of Kroger tomatoes, but the difference isn’t significant enough to warrant the exponential increase in price for the Cento stuff. This goes for almost everything else in the store. Buy cheap. Think outside the box. For instance a can of Hunt’s spaghetti sauce is going to be much cheaper than a jar of Ragu, but the cans are usually on the very bottom shelf and very often get overlooked. That goes for most things: the most expensive items in the grocery store are at eye level, so scan the bottom and top shelves for the cheap stuff. Don’t get caught up in food trends. Sea salt and/or Himalayan salt, for instance, is all the rage now (we were discussing this a different thread recently) but salt is salt, and buying a generic can of basic table salt will be cheaper than an equivalent can of Morton, which itself will be much cheaper than a Diamond Crystal box of Kosher salt. Get cheap stuff and look for sales and coupons which can save you even more money, as long as you compare prices and do your due diligence. Often name brands are what go on sale but even at sale prices they’re likely more expensive than the house brand equivalent item.
So start with your cheap ingredients and basic cooking skills and go from there. Learn to cook with what you have, not with what you want. If a pound of chicken breasts are cheaper than a pound of lean hamburger, make tacos with chicken, not beef. Pound for pound veggies are usually even cheaper, so learn how to incorporate lots of veggies into your menus. But again, do your due diligence. If broccoli is on sale, great! But since we (most of us, anyway) only eat the head how much useable food does a pound of fresh broccoli from the produce section going to actually give you? Half of that pound is probably stem. It might be cheaper – actually, it probably will be cheaper – to buy bags of frozen broccoli florets rather than the fresh stuff. Regardless, going meatless several days per week can really stretch the food budget.
If you have a large freezer, utilize it. Fill it with cheap cuts of meat, frozen veggies, and leftovers that can freeze well like soups and tomato sauces. If you have a small freezer, utilize it as well by freezing meats, veggies, and leftovers.
As you learn to cook start keeping a list of the ingredients you use the most. Always keep those on hand, especially if they’re shelf-stable. Beans, rice, pasta, canned vegetables, cold cereal, butter, olive oil, flour, sugar, baking soda, baking powder, corn meal, honey, eggs, cold cuts, and cheese are what we always have on hand because we use all of that stuff regularly. We keep our eyes out for good deals on any of that stuff and pick up the shelf stable stuff when it’s on sale, even if we have a supply of it already because we know it will get used soon-ish. This is cheaper than waiting until we need it and making an unscheduled run to the store and paying a higher price for it.
Find a few cookbooks that were written before food snobbery became de rigueur, such as an older Betty Crocker or Joy of Cooking (a copy of which you should have regardless). The recipes are simple, don’t require exotic or expensive ingredients, and are often quite good.
Now, even as you learn to cook you’ll find some things that come prepared from the store are just cheaper than making from scratch. A homemade spaghetti sauce can be divine, but that can of Hunts sauce will almost certainly be cheaper than the individual ingredients needed to make a homemade sauce. Which one is more important is an individual thing. Remember also that cooking in bulk may cost more at the outset but be cheaper per serving. For instance making a big pot of chicken soup will cost more than a can of Campbells, but you’ll get many more servings from the big pot (servings which you can freeze for later).
Think about meals that make good leftovers. Most Mexican food reheats well, same for stews and soups, as well as most casseroles. You can buy the cheap ingredients, make a big pot/dish of whatever, and the leftover go in the fridge or freezer to have later. That one expenditure feeds you for two or three days.
Plan ahead. Make a menu for the week, including lunches. You can do a grocery shopping on a Saturday and maybe do some simple prep on a Sunday, reducing your workload later in the week. For instance, maybe have a chicken salad for lunch on Monday and Chicken fajitas for dinner on Tuesday. Cook up your chicken and slice your veggies on Sunday and put them in the fridge, and that way you have much of what you need for both Monday lunch and Tuesday dinner prepared and ready. You can tweak your menu to fit what you find on sale that week. Did you score a helluva good deal on ground beef? Make meals that week using beef instead of chicken and save the chicken-heavy menu for a week when you discover chicken is on sale.