Down to the nit-picky questions.....
On the Island days that you hiked and snorkeled, did you just wear your swimsuits under your walking clothes?
Also, it seems there are several hours on the islands at a time. Was there any way to "go potty" during that time or do we need to be really careful with the coffee in the mornings?
Thanks!
No question is too nitpicky

As for hike, then snorkel days; there are 2 days where you do a "hike" before a beach snorkel. The first one is more of a hike and I'd wear your suit underneath hiking clothes and especially wear your good hiking shoes/sneakers. The second one was more of a "beach walk" which you could do with your reef runners/beach shoes and beach cover up on. The other snorkels; you'll head back on the pangas to the ship after the hike, you can get your gear (or drop off non snorkelers) and then go back out on the panga for a deep water snorkel.
Now the itinerary could change- but rest assured you will get a briefing every night at dinner with all the nitpicky details. They will literally tell you... bring this, wear that; you honestly don't have to use your own brain
On the potty issue...there is no eating, drinking and no ducking behind a bush on the islands. They are quite strict about it. Im sure if you were ill or a child really was stuck the guides would make some kind of arrangement, but really there is no "going" on the islands.
But with that said- you will find that there are very few island stays that last more than a couple of hours. Some can be more than 2 hours if you have a snorkel afterwards, but well, what happens in your wet suit stays in your wet suit

Also, there there are pangas going back and forth pretty frequently, so someone with a real issue could head back if needed (though who wants to miss all the fun!!) So we did find ourselves being careful, but at the same time you do want to hydrate. Honestly, no one in our group really struggled with this, luckily its only an hour or two.
I only had one issue, as I was hiking one day, I felt like my stomach was acting up, and sometimes when that happens I have to go, quick! One of my tips was to carry a tiny "go bag" of first aid and tummy remedies...you can find the list of stuff I bring in my review with the packing list. What I did that day was take an Imodium , with my water and the "feeling" passed and I could enjoy the hike. I don't usually do that sort of thing, but that day I was happy to have the Imodium with me. Ok enough Potty Talk!
Boy Kristalew, you must be leaving soon! So exciting!! I have most of these threads on "instant notification" so if you have any last minute ???s I'll do my best to get right back to you...have a blast!!!