BG, you might find you are happy to eat during your labour, in which case water would be just fine It's only if you can't eat that you need to think about your sugars, which I'm sure you know.
Like Janie said, you can keep lollies handy or jelly (though I found I didnt' even want jelly) but a lollypop that you can intermittently suck on is good. Or peppermint lollies which can really help ease nausea.