It depends. My first pregnancy, the reflux got worse and worse, culminating in THE worst during labour. It was horrible, all I wanted was some milk and there wasn't any available (this is germany - very few adults drink milk here
). I ate (toast i think) but then barfed and didn't attempt it again.
My 2nd pregnancy, I again had back reflux but somehow it disappeared right before labour. I ate and ate and ate during labour, only stopping a little bit before transition. I ate apples and shortbread cookies, maybe a yogurt (can't remember) and drank labourade. It was great for fuel - no reflux, heartburn or vomiting.
I don't think you can ever predict, so best to prepare just in case you want something and can't get it (i.e, my milk situation)