That said, my first rule of trail running is: Be prepared for the unexpected! Even the most seasoned runner can trip and break an ankle in Forest Park! How many of us have belly flopped on the trail after tripping on one of those pesky roots that seem to poke up out of the ground as we run past? Just last week I caught my shoelaces on a root on the side of the trail and landed gracefully perpendicular over a log about 10 feet past where I had tripped.
This brings me to some of the most important aspects of trail running: Always tell someone where you are going, especially if you are running alone! Know your route and approximately how long it will take you to complete the route. Have a check-in time and alternate plan if you don't meet your check-in time. Plan extra time for things like blown down trees, washed out river crossings and other random detours or re-routing events and let someone know of any plan alterations as soon as you can. Have essentials that are relevant to the destination and duration of your run. For example, if one is running the trails in Forest Park, one does not need a water filter, and might want to leave the big map at home. However, if one is running the Timberline Trail, then a water filter and map are absolute essentials!
On short (7-15 miles) adventure trail runs, I always carry 1-3 liters of water, snacks, sunscreen, lip balm with sunscreen, first aid (for me as well as my dogs), whistle, knife, cell phone and full map if it's an area I'm unfamiliar with. Most of the time I even have my headlamp and a light jacket in my pack! If there is any chance I could be out longer than I expect, or could be exposed to harsher weather during the day, even on shorter runs, I thrown in the emergency blanket, cell phone charger, packable pants, gloves, beanie, handwarmer, signal mirror and EXTRA snacks! I always pack at least 1.5 times the amount of snacks I think I'll eat, sometimes I eat half of them, sometimes I eat them ALL! A good personal rule is a snack every 3-4 miles, (which equates to about one snack an hour) depending on how far I'm going, somtimes more if there's a lot of elevation gain and I know I'll be expending a lot of energy. If it's a longer run and I know I'll have a water source, I bring the water filter as well. I also throw in Electrolyte tabs or mixes on longer runs. They aren't always needed, but sometimes, especially in hot weather, they can be a game changing bonk buster!
Basic Gear List: (should include, but is not limited to these items)
Garmin InReach or other Personal Locator Beacon
Doggy Trail Essentials (that are also always found in my pack):
Image pictured is everything that went into my pack for running the Timberline Trail in a single day, before snacks and a burrito were added to the mix.