https://rebrickable.com - A LEGO database that shows you which sets you can build from your existing collection, also includes thousands of fan-submitted designs.
ingredients:recipes::legos:designs
it would be silly to track things inside a refrigerator, but we could track purchases on receipts, and then calculate the amount over time using some smart-decay-rate. Cant assume it's gonna be easy to be able to live query the contents of someone fridge in real time - but can do estimations. Then people could add their recipes to a central server, and well, you've pretty much coded everything after that if I get your gist.
email me: jay@pitel.co