The crazy action sequence at the end with the dwarfs in the mountain - it seemed a bit far-fetched to me initially.
But then I remembered that we're essentially looking at a party of 10 engineers (plus Bilbo). They're good at problem-solving and for decades they've got used to making do with whatever resources are to hand. We saw Thorin and Balin in Erebor at the start of film 1 and they've never stopped thinking of their home, so I'd say it's safe to say they know the layout of Erebor really well, so they know where all their stocks should be.