Very much looking forward to our trip to Oahu and the Big Island starting next week! We're going on a couple of tours (specifically the Jurassic Adventure Tour, Climbworks Zipline and Night Snorkel with Manta Rays on the Big Island). I'm not usually one to book tours like these when I travel, so I'm not sure how much I should tip. I'm happy to be generous, but don't even have a baseline from which to start from. Any advice? Thanks!