[callum85]

You're not considering that a lot of people might just prefer to be explicit and specific about purchases. If I see I've run out of pasta sauce, I might want to scan the empty one to reoder it, because it's precise. I definitely wouldn't want to risk vagueness and inaccuracy just for the privilege of using an abstraction like saying "I'm out of pasta sauce" into a phone. What would that achieve anyway? Outsourcing the bit of your brain that says "we need more pasta sauce", so you've only got to worry about thinking "oh there's no pasta sauce"..? Scanning a barcode is simple and precise.

[scep12]

  risk vagueness and inaccuracy

You're scanning a barcode of an item you recently purchased from amazon. Where is the vagueness in querying for that item by type?

In most cases, your pantry has 1 type of each item, which means you've got a canonical mapping from "pasta sauce" to an item in your fridge. That also means you've got a very high probability of mapping the recent purchase of pasta sauce to the query of "pasta sauce." Where is the vagueness?

In the worst case, you've bought two or three different types of pasta sauce, and you'd like to replace just one. Let's be clear - this is most definitely the exception to the rule. In this case, your phone gives you a list of options to choose from -- the list of your N most recently purchased pasta sauces (backfilled by prior orders or popular choices).