The right equipment can make a day of hiking an extremely enjoyable experience. The wrong equipment can make you feel like you are on a death march! There are a lot of equipment lists on the internet that call out everything you need to have a safe hiking experience, but a lot of these lists don't explain why you need these products.
There are twelve "must have" items when you go for hike, even if it is in familiar territory and only for a short time in perfect weather. There are another ten optional items that you should carry when you are hiking. No equipment list is perfect. Keep in mind that if you are going for a day hike in the Painted Desert in July, your needs will be much different then going on a day hike in the Garden of The Gods State Park, In Colorado, or Acadia National Park in Maine.
The twelve "must have" items should be carried at all times. It may seem ridiculous to carry rain gear in a desert, but if that sudden shower were to come up, you will be glad to have it. You may have hiked an area one-hundred times and know it like the back of your hand -- but find out about an unexpected trail closure, and you will be wishing you had a map.
Naturally you will also need a pack to carry your equipment in. A well thought out packing and equipping job can allow the hiker to hold the twelve essentials in a small fanny pack. If you are hiking in special conditions like cold weather (which will require bulkier gear) then a day pack may be required. High quality day packs can be had for $50 to $75. Generally if you spend less than that on a day pack, you are risking getting a lower quality product, or worse one that beats you to death when hiking.
Number one, a plan. You should never hike without a plan. You should plan your route, check the local weather, get trail conditions, and notify a friend, relative, neighbor, or ranger of your plans. If there are trailhead registers on the trail you should use them. Try to stick to your plan.
Number two, a map. Even if you have hiked a trail a hundred times, you should carry a map. Unexpected trail closures, an injury requiring a shorter route, bad weather, or animal encounter can all result in a sudden change of plans. Having a map assists in this greatly. You don't have to carry topographical maps for a regular day hike. Practically every state and national park provides hiking maps of trails and features for free or a nominal fee. Some of the best maps I have ever used I paid 25 cents for at Yellowstone National Park, and they are some of the most low tech maps you will ever use.
Number three, a compass. Carrying a compass with you is not enough, you need to know how to use it properly. Adjustments for declination, field interference, the metal on your equipment, and poor handling can make a compass a dangerous tool to use. You should find a good orienteering class and take it to learn about using a compass in the field. If you do not have experience with a compass, you should stay away from lensatic models (ones with a flip up view finder) until you have more experience, and further they don't work very well when overlaid on a map.
Number four, a pocket knife. I am partial to the Swiss Army style knives, but almost any kind of pocket knife will do. You should keep your blade length around three inches and the knife should have a locking blade. A pocket knife can have a million uses in the field as the need arises. You should carry your pocket knife on your person, and not in your pack.
Number five, a whistle. A good survival whistle is essential to carry when hiking. The sound a whistle makes travels much further then your voice ever could in an emergency situation. When walking through bear country you can blow on it to alert the bears that you are passing through. You can also use it to communicate with others in your group, say some one is too far ahead, or falling behind. A whistle can be the best $2.00 to $7.00 piece of hiking safety equipment you will spend. You should always carry your whistle around your neck, and not in your pack.
Number six, a personal first aid kit. A good first aid kit does not have to be large, elaborate, or expensive. The basic kit should include antiseptic wipes, sting relief, burn cream, band-aids of various types and sizes, cotton balls, sterile pads, gauze, tape, pain reliever (a.k.a. aspirin or Tylenol), antacid (tablets), Benadryl (tablets), mole skin (for blisters), one pair of latex gloves, and tweezers.
If you are hiking in an area with a large poisonous snake population and will be more than one hour away from help you should also carry a basic snake bite kit but only after receiving proper instruction on it's use. A snake bite kit in the wrong hands can cause more damage then the actual bite.
Oral Benadryl should be carried for insect bites or stings. If yourself or a person in your party has never had an insect sting before (a.k.a. bee, wasp, hornet) the Benadryl can be administered to slow down an allergic reaction, but medical attention should be sought out at the first sign of a severe reaction.
You can contact your local Red Cross Chapter for basic first aid courses that can be completed in half-a-day and around $25.00. A good basic first aid kit can be found for as little as ten dollars with a waterproof container. A basic snake bite kit can be found for as little as five dollars.
Printable equipment list for day hiking...
Essential items number seven through twelve...