My labours were short I was not thirsty or hungry in any of them.
However, I did prepare by getting some Lucozade for some energy if I wanted it.
And I would have had some sort of protein bar and snacked on that if I needed to.
I've also read that chewable calcium tablets are a good idea if you're having a long labour. Boosts energy and helps encourage things along if I remember correctly...
The day I went into labour with my last, I was pretty sure I was in labour so I think I nibbled on a couple of slices of toast in the morning and just kept my food intake small and often.