1:) I find peppermint really helpful. Here in the Ozarks, there are quite a few roads that make me think of rollercoasters, and sucking a peppermint or chewing peppermint gum makes me feel fine.
Just make sure it's not "peppermint flavor", but real peppermint.
2:) I had a pair of pressure point bracelets once that applied a slight pressure to the underside of your wrists, in-between your veins. I don't know how solid the science here is, but psychological or not, it helped me.
3:) And finally, sitting in the front and looking straight ahead has been the best help for me.
Hope these help you enjoy your trips more!