i would say grains make up 7/8th of my diet, I buy frozen vegetables because fresh produce is more expensive and i try to keep the meet frozen till use, and i am not paying for utilities directlyAssuming you have routine access to a kitchen with adequate storage, functioning appliances, and working utilities:
Don't stock up on shit you won't use. It's probably a bad idea to buy a 50lb bag of rice if you aren't already in the habit of cooking and eating rice dishes. Establish the habit first and make sure you'll stick with it. Otherwise you'll just be throwing out a shitload of infested rice.
Unless you're one of those people who sees bean weevils and thinks meh, extra protein, you will want to commit to keeping a very clean pantry and make sure your kitchen hygiene is on point before you invest in bulk staples. Research how to store your provisions to keep pests out and prevent spoilage. Divide your purchases into smaller containers, so if one gets contaminated, becomes infested, goes bad, or spills, you'll only be throwing out a relatively small amount of food.
Every week, try to put aside a portion of your grocery budget for one spendier pantry item like olive oil, chili oil, miso paste, gochujang, soy sauce, hot sauce, or whatever spices you like. Once you build up a library of flavors, you can coax more variety out of your inexpensive staples and your thrifty ways will be more sustainable. That is, unless you like eating the same predictable meals day in and day out, in which case enjoy your autism.
It's a good idea to buy produce at peak season when it's cheaper; what's the best value at which time of year will vary based on where you live, and you can probably find a handy local produce guide online. Sometimes, you buy produce only to find that its texture is off, it doesn't have much flavor, or it's about to go bad. Learn how to roast, season, macerate, or hide these disappointing purchases in other recipes, or else you'll just push them to the back of the fridge until they go bad and you end up wasting them. It's easy to prepare quick, simple, delicious meals with fresh, high-quality ingredients, but learning how to make something palatable out of suboptimal provisions is trickier. Compare prices between fresh, frozen, and canned fruit and veg, and challenge yourself to use the tougher or less palatable bits like leathery beet greens or fibrous broccoli stems.
In a similar vein, I'm sure you've noticed that a lot of inexpensive ingredients tend to be dry, tough, or fibrous. These attributes make them cheaper and easier to harvest, transport, and store, but you'll often have to cook them longer to end up with something palatable. If you pay for your own utilities and especially if you are cooking for one, consider investing in a small slow cooker. For example, you can prep dry beans for a few meals without ending up with an absurd quantity of beans because you tried to optimize energy use, and without heating up your house in the summer.