As Snoklr45 stated, do the research ahead of time. There are many places you can walk to from the pier to snorkel, such as in Grand Cayman. We will also take a bus or taxi too to a beach and DW will swim on the beach while I do some snorkeling. When on a beach park yourself near some rocks that is where the best snorkeling will be.
I never had to wear a life jacket when snorkeling on my own. Mask, snorkel & fins all lay flat in the suitcase & will not increase the weight by much.
O F C'er