Here are a few of our favorite new items to help keep you going while you traverse beaches and rainforest trails in the tropics. (Note: Our reviewers field test everything that we feature, and we never get paid to endorse any product.) 5127 Osprey’s Meridian 60L bag ($350) is ideal for international birding: The carry-on comes with a detachable daypack, fits a week’s worth of clothes, and has hardy wheels that handle rugged terrain with ease. When the going gets tough, hidden straps transform it into a backpack. 5122 The new Peterson Field Guide to Birds of Northern Central America ($21) is worth the extra pound it'll add to your luggage. Packed with more than 800 species accounts, illustrations, interesting and useful info about behavior, and range maps, it's simply the best guide out there for Belize, Guatemala, Honduras, and El Salvador. 5123 Worry about finding rare birds, not the state of your drinking water. Whether...