– I don’t think they really need socks :-)
– once she was two months old we started using sunscreen with mostly zinc oxide as the active ingredient. That’s what our ped recommended – they won’t be labeled as safe for kids under 6 months because no one will ever test on kiddos that young. To avoid using too much, we rely on rash guards, hats, and shade.
– I think for sleeping at first you can use a cosleeper between you and then later a mesh leecloth to turn the v berth into a “crib”. Combined with a relatively firm v berth mattress I think you would be ok. I realize cosleeping is controversial, but for breastfeeding and with sides, it’s what we ended up feeling most comfortable with but YMMV
– We have two milkbarn swaddling blankets – they are the perfect size and weight for warm weather. I would think any muslin blanket would do and they take up hardly any space!
– cloth diapering for the first few months is easy! We found that prefolds with covers was easiest for us, the poopy ones can pile up without smelling too bad, and washing them is a breeze. We stick them in the dryer which is apparently a no no but haven’t had any absorbency issues yet. When munchkin was a newborn she was too small for any of the cloth diapers, so you may need disposables depending on how tiny the little one is (ours was around 6 lbs). If you are not planning on breastfeeding (or it doesn’t work out) formula/solids fed poop is much stinkier so I don’t know how cloth would fare onboard then.
– Baby wearing has been a lifesaver, I haven’t checked your registry but I would definitely recommend an ergonomic breathable one.
– the Stearns infant puddle jumper was the only life jacket Marcella would tolerate. We tried 6 different ones. Which is just to say, you might have to be patient to find the right fit!
– we haven’t tried this yet, but we plan to rig something up with a couple of dowel rods and sturdy fabric that can go across our cockpit to kind of cradle her. Will let you know how that goes! Like a hammock style device that can kind of cradle her on a boat when we’re above deck.

You honestly don’t need much! As they get older they can play with measuring cups, etc and they learn so much just by exploring their world! The nice thing is that boats are already mostly baby proofed, since everything needs to stay shut/together when you’re underway. Good luck!!