Birding/animal watching: don’t forget a good pair of binoculars. If you’ve got extra cash to splash, you could even opt for digital binoculars with the ability to record what you see. The Sony DEV Digital Recording binoculars (store.sony.com) record video in full HD resolution, meaning you can have proof to back up your boast of having spotted saltwater crocodiles Down Under.
Hydration pack: you could carry water in a bottle or a wineskin. However, if you like keeping your hands free while hiking, a hydration pack such as those made by Camelbak (camelbak.com) is perfect. It’s essentially a tube threaded into a water sac that is stuck in a backpack…though we don’t recommend drinking from the pack while using both hands to clamber between rocks.
GPS: yes, you can use your iPhone or smartphone as a GPS (assuming you purchase proper software and not rely on the inbuilt map application which will not work if you lose mobile-phone connectivity). However, many smartphone apps are not built for hiking and have poor battery life. Consider a dedicated handheld GPS unit such as those by Garmin (garmin.com) or Magellan (magellangps.com). These units have detailed topographic maps and are rugged enough to survive being dropped. It also doubles as a compass.
Stop leeches: if you’re hiking into leech terrain, take some precautions. While there isn’t a fail-proof method against these bloodsuckers, hikers have had success with a variety of methods and gear including using strong insect repellent or eucalyptus oil, wearing leech-proof socks, waterproof boots, leg gaiters and carrying a stick tipped with a salt-soaked cloth (apparently, leeches hate salt so if you see one, touch it gently with the cloth).
Trekking poles: hiking sticks, walking poles, whatever you call them, some hikers swear by these to generate a good rhythm as well as provide support on steep terrain. We’d recommend leaving them at home unless you really need them (for example, if you need support for a bad knee, you’re going through particularly tough terrain, and so on).
Essentials kit: pack a basic first aid kit, some matches or a lighter, and perhaps heat packs if it’s going to get cold at night. Also keep a knife and torch/headlamp in your pack. If you’re hiking in wintry or icy conditions, an ice pick and extra set of clothes will help too.