I use the following as a rule of thumb for calculating how much time to allow for a day hike:
- Easy: 20-minute mile average pace (3 miles per hour)
- Moderate: 30-minute mile average pace (2 miles per hour)
- Strenuous: 45-60-minute mile average pace (1-1.5 miles per hour)
I do NOT generally consider any hike that requires rock scrambling or hand-over-hand climbing to fall within the category of a "day hike."
What you decide to pack will determine what kind of pack you need. For hikes of 30 minutes or less, no pack is necessary. For hikes of 30 minutes to 2 hours, I would recommend a "fanny pack" or hydration carrier (a "Camel-back"). With the latter, you can shove several things into the carrier and attach other necessities to it. For hikes of 2-5 hours, I would recommend a standard day pack (i.e. military-style "assault pack"). For anything over five hours (ten miles or more), I would recommend a military-style "ruck sack" (aka "Alice pack" or "MOLLE") or a commercial backpack. An alternative is a combination of an assault pack and a hydration carrier (or military "Load Carrying Equipment").
1. Water. My general rule of thumb is to take one pint (.5 liter) per mile in warm-to-hot weather. If you begin hydrated, and keep some post-hike water at your start/finish point, then you may be able to get by with less than this. On the other hand, if the weather is exceptionally hot and/or if you are carrying much of a load, you will want a quart per mile.
Given that water is heavy, I recommend that the average person take water purification tablets or another method of collecting and sanitizing water if their water needs will exceed a gallon (naturally, the amount of water each person is willing/able to carry will vary significantly). The tablets (or iodine) take time to work. The alternative will require starting a fire, which isn't always an option. Most important is to always begin any hike fully hydrated.
2. Signaling Device. I always hike with a whistle. Whistles work day and night, don't use batteries, don't require a line of sight, and don't mimic nature. On the visual side, a signal mirror is a lightweight, and energy independent, signalling option (for daytime). For nighttime signalling, flashlights and chem-lights are good options.
3. Clothing. A poncho is a good lightweight way to be prepared. A poncho is generally water resistant--not waterproof--but it is still of use. If draped over something, ponchos can provide shade (if necessary) and shelter. Other clothing worth packing on a day hike include: clean, dry socks, a dry t-shirt, and windbreaker (or rain jacket).
4. Fire starters. It is never a bad idea to carry a lighter--even on day hikes. I usually carry a magnesium bar and some tender (petroleum jelly-soaked cotton balls work great) on hikes longer than five miles. I haven't needed this yet but, for the weight, it just makes sense.
5. First-Aid. It's not likely that you'll need much in the way of First-Aid on a day hike but preparedness is never a bad thing. I would recommend some moleskin, some alcohol (or alcohol wipes), Band-Aids, and an instant ice-pack. Unfortunately, Murphy's Law tends to rear its head. Whatever you need is what you didn't pack. Such is life...but pack the most likely items just in case.
6. Cordage. For day hikes, there is no compelling reason to take cordage. That being said, 550 cord is light and it wouldn't hurt to have 50-100 feet in your pack. With a couple of bungees and a poncho, you can have a decent shelter in no time.
7. Cutting tool. I take a folding knife and a multi-tool pretty much everywhere. I take a larger fixed-blade knife on most hikes as well. You probably won't need any of them but, let's face it, all survival situations are unplanned. If it's planned, its not truly a survival situation.
8. Food. I would recommend undertaking any day hike on a full stomach. I would not bother taking any food on a hike less than 5 miles or so. Pack a snack for 5-8 mile hikes and a meal (perhaps an MRE?) for those from 8-12 miles.
9. Containers. In addition to canteens (or your water bottle/hydration carrier of choice), I strongly recommend a metal canteen cup. These can be used for boiling water and for cooking. You probably won't need it but, if you do, you'll thank me.
10. Navigation Aids. A compass is not necessary for day hikes on marked trails but a basic one will help you find the trail if you happen to stray from it. I would definitely take a trail map, preferably a topographical one (if you can find one). Here are links to trail lists/maps along the Blue Ridge Parkway, courtesy of blueridgeparkway.org:
North Carolina BRP Trails
Virginia BRP Trails
The bottom line is that you can never be fully prepared for every contingency. What you can't afford to risk is dehydration or hypothermia (or hyperthermia). Thus, take enough water and a way to stay dry/warm. In the event that you get lost, you will need a signalling device (preferably audio with visual as backup). Most of the other items on the list vary based on the distance of your hike. One thing I didn't include--but is always worth taking--is a cell phone. It may not work...but it might. Why NOT take it?
Happy hiking!
Chris
(aka BRP Hiker)