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).