It's probably not the DXM making you puke if you're using coughgels. It's all that gelatin, food coloring, and god knows what else. I've puked using them before. To avoid that I'd do this: eat them on an empty stomach with only clear liquids before/during the trip. Coke and drinks with food coloring in them will encourage vomiting. Having a stomach full of food will bring it on pretty quickly as well.