Ginger is an ancient remedy for motion sickness, I use it all the time in my travels to Panama as the pilots of the little island jumpers don't really have a concept of turbulence avoidance. Finding real ginger is sort of tough; Ginger Ale doesn't really have ginger in it anymore, and you can't really get it from the drugstores.
The best bet is, about an hour before you start the rides, go to a chinese restaurant and order a large helping of Ginger Chicken. It will both fill you, helping you to avoid the costly food prices at the park, and also ensure that you will not get motion sickness.
Have fun and thank me later!