Opinions on Lenses

I thought about asking everyone on here first.....I will be traveling to Costa Rica later this year for my sisters wedding. I have a Canon Rebel XTi and have the lense that came with the camera 18-55mm and a Canon 75-300mm lense. I would love anyones opinion on lenses that I would possibly like to use for the trip for some unique pictures. I was thinking of trying www.borrowlenses.com but have not rented anything yet. I am a self taught photographer and I know that there is much more for me to learn but I would just love to take some awesome pictures while down there. Thank You!