In addition to all the excellent advice, I'd like to recommend a few other things that help me. I have a digestive disorder, as well as an inner ear disease which causes the type of vertigo commonly experienced on moving boats.
As @jrovermier mentioned, ginger has been medically proven to help nausea, and I rely on it every day. I recommend sipping on tea made from 100% ginger root. It's caffeine-free, safe for breast-feeding, and can be either hot or iced. Tea bags are easy to pack, and if the taste is too strong, buy some sugar packets and pack them together. Peppermint also helps nausea, and adding a 100% peppermint tea bag is a good way to temper the strong ginger flavor.
For convenience, my favorite product is Tummydrops, which are individually wrapped lozenges. Even tough they're made with real ginger, they don't have the harsh flavor that can make raw or candied ginger hard to swallow. For me, they work quickly and are more effective than ginger capsules.
Ginger tummydrops contain a patent-pending specialized blend of purified gingers that are enriched in the special compounds that can help soothe nausea and digestive upsets. Each ginger tummy drop is made from the purest and best tasting ginger, which may assist with occasional stomach upset, nausea, morning sickness, & motion sickness. They are great for travel and when you're on the go, and always keep your tummy happy!
They're low in sugar, have no high-fructose corn syrup, are gluten-free, kosher, non-GMO project verified and made in the USA with only the most premium ingredients! The NATURAL choice for upset tummies™
They also have a peppermint drop. It's made from real peppermint oil, which, as I mentioned about the tea, is helpful and soothing.