Certain destinations require special equipment. In the past we've tried to scrape by spending the minimum on things like this. Don't. If you are traveling somewhere just to do one thing, then spend some money to make sure it goes well. That includes gear but also guides, training or anything else you need to get the most out of your adventure.
Before we went on safari in South Africa we were told that we HAD to have a pair of binoculars. A bird watcher friend and native South African told us to literally not bother going if we didn't have binocs. This left us in a difficult circumstances. We will probably never go on safari again, so did we really want to drop a whole wad of cash on something we wouldn't use ever again? On the other hand, if this is the only time we do this, did we want to scrimp and end up compromising our experience?
In the end, I found a used pair of Monarch 5's on Cape Town's equivalent of Craigslist. We bought them for $180 and sent them home with Jess' Dad to be resold on Ebay. If we can get $150 for them (new they are $280) we'll have 'rented' them for a few weeks for just $30. A pretty good deal.
As it turned out, you really do need them for wildlife watching. In retrospect, I would have brought them on the cruise ship as well. Being on the top deck was a lot like being at the top of a building and it provided great views of cities and landscapes. Binoculars would have improved the experience.
Jess bought me this for my birthday this year to make surfing easier. I haven't been able to surf as much as I wanted to but it turns out this is great for a variety of water activities. I've used it for distance swimming in cooler water, snorkeling in heavy sun and in place of a full wetsuit for diving. If you are fair skinned, plan a lot of water activities or think you are going to want to learn to surf, you may want to consider picking up a rash guard or wetsuit shirt.