Why not volunteer while you vacation? There are so many opportunities around the world to offer a helping hand while you explore and enjoy their environment. A beach cleanup in the Caribbean, a children's project in South America, or participate in the Mālama Hawai'i program with beach conservation, tree plantings, or restoring a native fish pond.
There are numerous properties around the world today that offer sustainable accommodations. Some of these could be "green" hotels that have made environmental improvements to lower their impact. Others are accommodations that are literally built into nature with sustainable materials, offering a natural way to stay and enjoy the environment ~ leaving only your footprints behind.
There are many eco tours available that replace the traditional safari, in which you can visit gorilla or other wildlife preserves, or a relief mission to an animal clinic. All the while, observing the animals, and helping local conservation programs that fight poaching and hunting.