A room card holder ( lanyard ). Umbrella stroller for your toddler ( smaller the better). I take a water flask with me for port days. Copies of your passports. If you like to snorkel get ur gear with u instead of renting. Floaty for toddler, hat, sunscreen and a fan.
Dramamine patches ! If you forget everything even clothes ! Don’t forget Dramamine patches and that little one can wear one too
Take something for seasickness! Not sure if they make seasick meds for toddlers but might be worth checking into.