casey, ginger has been researched and confirmed by NASA. Who also point out that something like 1/3 of the meds work for 1/3 of the sufferers 1/3 of the time, there's no universal cure for motion sickness.
Ginger is classed as a "rubefacient" something that makes your skin pink because it is expanding the capillaries. Which in turn increases capillary blood flow and oxygenation and the extra oxygenation is one mechanism to reduce motion sickness. That's why exposure to alcohol, carbon monoxide (tobacco smoke) and diesel fumes all seem to make motion sickness worse, they decrease oxygenation.
The salt smell...he's just seven, he doesn't know what's going on so he tries to rationalize it. There is some lavendar-and-whatever bogus potion that you are supposed to put behind your ears to reduce seasickness, and if part of this is in his head that might help as it indeed changes the smell and lavendar tends to be calming.
Wrist bands that push on the neh-kwan (sp?) point work for some people. And the electric wrist reliever works well enough to be FDA approved for morning sickness. That's probably the most effective non-drug solution other than taking up golf. But it does depend on being positioned very precisely, and then KEPT in position.
Giving him something to keep himself busy, pre-occupied, and eyes out of the boat, all will also help. Good luck!