We brought our son for his first trip at 6 months. We brought the smallest pack n play available. It was really tiny by comparison and worked great. Had a life jack as well which we tested prior to our trip. Brought our baby monitor as well since the boat had a generator. It really was easy. Just one person watching him at all times when he was awake. Just held him on our lap in the dinghy rides. We even did a little hiking.

Here's a selfie of him while hiking

https://photos.app.goo.gl/apafHWg3NsQgUJAK8