I take Ginger Root capsules, a natural supplement. I take at least one every morning and at least one every evening as a preventive. If I have experienced motion or if it looks like there will be waves above 4 feet, I take two of them at a time. I start one week before the cruise with one in the morning and one at night and I continue for two nights after the cruise.
I also have Bonine (or Meclizine by Rx) in the 25 mg dose if I need it. My Mecllizine Rx says 1 tablet every 4 to 6 hours.
I also have some of the inexpensive wrist bands, but I haven't noticed consistent relief from them. I use them as my third line of defense if I still have trouble after the first two.
You can get ginger ale from the restaurants or lounges aboard the ship.
You can get Bonine from the medical facility on deck 1 and often from the Guest Services desk in single does packages, both without charge.
On our last cruise, my DD was feeling seasick and I called room service and asked them to send up plain toast and plain crackers and she said that helped too.
Fresh air and looking out at the horizon helps me visually. NOT focusing on a stationary object while the ship has even slight motion helps. NOT watching the swimming pools to look to see if they have 'echo waves' is also a good idea. NOT eating large meals also helps.
hope that helps