Things without expiration dates, like fruit and veggies don't follow a particular timeline. They might be bad in 2 days, or 2 weeks. That means they can't be used with this application either, since they go bad when they look bad.
But, what about frozen dinners or something that I prepare, and freeze for the future? Well, I'll just write the date on them, when I stick them in the freezer.
Congrats on the experiment, but I'm going to be a little harsh on the concept and say it should be renamed to wastetime.io. This looks like a huge time sink by inputting everything I buy, and then removing everything I use. Apps are suppose to achieve the opposite, they should save me time.