Yes, I buy and cook all the food for my family of four. However, I remember there were a lot of food items that I could never really make work for myself when I lived alone because I could never eat it fast enough to get through it before it went bad.
It is a lot easier now that I have four people to feed, although the issue now is more that our two kids are insanely picky eaters and it is so hard to find meals everyone can eat.
What you describe in your first paragraph is something I hear very often from people that always eat out and don't want to learn how to cook their own food, because for them it's not worth it, due to the reasons you mentioned.
I'm really curious, what are the items that you couldn't make work living by yourself? I personally cannot remember many of these instances back when I cooked just for myself. Most of the food items I had could be frozen or turned into a dish that in the end could be frozen well.
It is a lot easier now that I have four people to feed, although the issue now is more that our two kids are insanely picky eaters and it is so hard to find meals everyone can eat.