I would pack a small ziploc with some of those individual packets of powdered Pedialyte. They can be added to bottled water to reconstitute. So much better than lugging those big bottles of Pedialyte in your suitcase, and they really help to keep the lil one hydrated during the hot days. Instead of a life jacket, you might want to consider getting one of those all in one swimsuit with floaties built in. This one has the advantage of SPF+50 sunscreen built into the fabric: http://www.amazon.com/Floating-Swims...ref=pd_sim_t_4
The stroller might be helpful to you in the airports, because you can safely strap him in without worrying about him in crowds and you won't have to carry him around. Also, you can easily gate check it when you board the flight. However, I don't think it will be that useful in the sand, or that safe to use on the sides of road with those crazy fast drivers!
Just try to keep your little one in the shade as much as possible, and keep him hydrated with fluids. You will both have a wonderful trip!!!!