You don’t have to pack hand sanitizer - Sanitizer does *not* protect from norovirus. Old fashioned soap and water is needed for that.
Bring your preferred cold medicine(s). Often, trying to find <drug> in the gift shop or in port is a lost cause. - But you can get Dramamine for free from the ship’s doctor.
You're going to get cruise crud no matter what. Bring some cold medicine with you and take it at the first hint of illness.
If you're prone to tummy upsets AT ALL bring stomach meds. Stomach meds are usually not available on the ship because the ship wants you to go to medical for stomach issues
Wash hands all the time with soap and water for at least 20 seconds.
Whenever possible, use the bathroom in your cabin, not the public ones.
Take vitamin C daily (or drink OJ, whatever works for you)
Eat yogurt daily (the vit C and probiotics can really do a number on bugs)
If you get sick - GO TO MED BAY. If they *make* you stay in your room, the mini bar and PPV TV become free, and Royal Carribbean will comp some of your trip (not sure about the HAL policy)
“Liquid Comfort Noodle Soup” delivered to your room can help tremendously when you feel cruise crud coming on, or after an evening of indulging in Wang Wang.
The biggest vector for germs are your face and hands. Avoid touching your face, particularly if you wear glasses. Avoid eating with your hands whenever possible unless you have just washed them. There are utensils available on the Lido and Main Dining Room.