Hydration: Running in nature means you're probably not going to pass by any water fountains, and because the terrain is more demanding, you're bound to work up a thirst quickly. For all but the shortest of trail runs, carrying a hydration system is highly recommended. Hydration belts, hand straps for handheld bottles, and hydration backpacks are all good options. Choosing the right one, however, depends on your personal preference and other factors, like how long your typical trail runs are and how many other items you want to carry with you.
Specialty Items: For longer runs through certain types of terrain, there are a few other items that may be necessary—or at least nice to have. In densely forested areas where you'll be making slow progress, bug spray can keep you from going crazy. It's nearly always a good idea to have a lightweight first-aid kit on any run. If you're planning a multi-day adventure run, or if you run in the evening, a headlamp is a must. For very steep or rough terrain, trekking poles may be useful. Finally, you might need a well-fitting, vest-style backpack to carry all your extra goodies.
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