I only buy packages, containers, or cartons that will sit within my nutritional budget to eat all of in a single sitting. One, maybe two of those = one meal. Especially those wonderful single-course entrees I can buy at ALDI for like six bucks a pop. That's actually a day's worth of food. Especially because I tend to eat one meal a day (when i am behaving).
Costco rotisserie chickens rock my fucking world too. Those things can be more than one meal!
I will also buy packages of "salad mix"--mixed greens with a few other veggies in it,
and then I'll add a nice dash of salt, and either a splash of apple cider vinegar or a liberal dusting of Parmesan cheese and a sprinkle of red pepper flakes, then shake it all up and just GO TO TOWN on the whole container.
The only perishables I buy are things of this sort that I will most certainly eat RIGHT AWAY.
Everything else is either
a: canned goods where i'll use the whole can at once adding to one of the above items
or,
b: non-perishable usually dry goods with which i can augment other things with pinches and dashes at a time (there are some things like vinegar or certain hot sauces that age and develop more flavor over time).
Well, there certainly are """"people"""" (Nationalist Christians, aka Nat-Cs) who think I am skilled and experienced at eating babies, so... I guess???
If you're doing 1-a-day, a rice cooker can be a great simplifier. Throw a measure of rice & your protein into the cooker, some rough chopped veg if you like. 2 minutes prep. While it cooks, make some kind of a sauce - yogurt or mayo make great bases, just add whatever spices you like; gochujang or miso thinned out with some soy sauce, citrus, or vinegar. When the rice & protein is done, pour on the sauce, add some pickled veg if you like. 800-1000 calories, depending on how much fat is in your sauce, one cooking pot, one eating bowl. 20 minutes start to finish.