Honestly, I guess the difference between how much food a whole family goes through and the amount that one or two people go through. When buying for your family or for roommates, a standard bottle of milk or loaf of bread will be gone in under a week. On your own? You might get through half of that if lucky, with plenty left over going to waste.

So you have to really reconsider how much you'll be able to eat/drink before it expires, and often buy way smaller portions than you would if shopping for others.