Re: Devil's advocate says...
I think we're far more likely to see ubiquitous RFID tags on everything that has a sell-by or use-by date. In 5-10 years (thinking the average expected lifespan of in-service fridges) I can easily imagine RFID tags being cheap enough to stick on anything from a carton of eggs to a container of yogurt. And if they're cheap enough for that, then they _will_ be on everything, because of the stock-keeping hassles it will reduce for wholesalers/retailers.
So then it's just a matter of your fridge inventorying everything that goes in with an RFID tag. _That_ technology is already cheap enough. Obviously it won't be able to keep track of your fresh vegies, but it can track anything packaged. And assuming you don't put empty packages/containers back in, it can tell you (for instance) you're out of butter. (It won't tell you that there's only enough left for one slice of toast tomorrow morning - at least not at first.)
And who knows, maybe someone bright can figure out a way to use resonance or path timing or who knows what other emergent phenomenon to get a liquid level off a container with an externally-applied RFID tag at a known position. There's loads of people way smarter than I am; I'd be daft to say it can't be done.