My personal miracle nausea cure, ginger beer.
I can't get enough of the stuff, and it cures nausea incredibly quickly. Even if you don't like ginger beer, just keep a bottle of it in your bag, just in case. When you feel nauseous, take a drink and it should subside. Also, don't get the super cheap stuff, it doesn't need to be expensive, but make sure it's not suger-free, or uses any kind of artificial sweeteners instead of proper sugar. I've found that sugar-free ones actually make the nausea worse.
Also, try not to think about it, so put yourself near friends who you can hold conversation with for a long time, and keep yourself occupied. If you start to feel sick, if you're reading or anything like that, stop, as it can worsen the nausea.