Shorty wetsuits with short sleeves are provided. They were warm enough for the regular snorkeling in September (when we went), but for the deep water snorkeling, my husband wore a midweight neoprene rashguard and a cap. They also provide flippers, masks, flotation vests and snorkels; no need to bring your own. After snorkeling, your wetsuits are hung up on hangers on the Marina Deck and your snorkeling gear is hung in a mesh bag. I have no idea if wetsuits are sanitized, but don't see this as an issue.
We had wet and dry landings and neither are a problem. You can bring water shoes and change into regular shoes on the beach. There are towels available on the Marina Deck where you board the zodiacs and you can take one to dry off your feet in a wet landing. I think we only had one wet landing.
The gift shop is tiny; no sunglasses, no sunscreen, no first aid items (that I recall) and a few hats and shirts. Bring what you think you will need. There is a better selection at the airport when you land, so you can grab anything you forgot there.
The ship does have walking sticks if you need one.
The bathrooms have soap, shampoo and conditioner, as well as two water bottles and a dedicated tap for filtered drinking water. Do not drink tap water in Ecuador.
There is no dress code and you absolutely do not need a jacket for dinner. I never saw anyone wearing one on our cruise. A nice pair of pants/skirt or dress and a shirt/blouse are fine. This is a casual expedition cruise; no one cares what you wear.