Number seven, a flashlight with spare batteries.  The large lantern style flashlight has been replaced by micro flashlights with alloy skins, xenon bulbs, and a battery life of eight hours on two AA batteries.  You should carry a flashlight with you regardless of the time of day your are hiking or your plans.  A severe storm can require you to stop while you wait for it to pass.  What would you do if night fell and you did not have any light.  It is also essential to carry spare batteries that are known to be fresh.  A good, reliable, compact, waterproof flashlight can be purchased for under $20.

Number eight, waterproof matches.  Carrying waterproof matches is done to expect the unexpected.  If you become lost, delayed, or injured, a day hike can turn into an overnight stay in the wilderness.  Accidentally fall into an icy river, or get pelted by an unexpected rain storm, your ability to make a fire to warm up may mean the difference between life and death.  Genuine waterproof matches should be carried.  If you transfer your matches to a match holder, be sure that you have a surface to strike the match on if a special surface is required.  A cigarette lighter is not a good substitute for matches, but can be carried as an alternative source of flame.  If you want to feel truly prepared, you can carry a flint and steel kit with some cotton and cork for fire starting as a third backup.

Number nine, emergency rain gear.  Your equipment does not have to be elaborate.  A simple poncho left in it's store packaging is more than adequate for most regions of North America for three season hiking.  If you are hiking at high altitude, in an area that is prone to rain a lot (the Northwestern United States, New England coast, Northwestern Colorado, Southeastern United States in the spring and summer) or where the temperature will be below 60 degrees, more adequate rain gear should be carried.  If you are caught in a sudden shower you should cover up in your poncho, and wait for it to pass.  Make sure you are not standing in a dry riverbed or wash while waiting.  If you are caught in a thunderstorm you should move away from high ground and tall objects (like trees) immediately.  Find a low spot, ravine, or thin place in the woods, cover up with your poncho, stay low and wait for it to pass.

Number ten, insect repellant and/or sunscreen.  The joy of hiking, fresh air, scenic vistas, ticks, chiggers, mosquitoes, and sunburn.  Insect repellant and sunscreen are vital to carry when hiking.
 
When using insect repellant it is best to treat your clothing with a spray before entering the field, and to use a cream based repellant on any exposed skin upon entering the field.  Cream based repellants pack better and take up less room.  A variety that contains anywhere from 20% to 35% DEET should be effective in most cases.  DEET masks carbon-dioxide which most biting insects use to detect their next victim.  DEET in high concentrations (a.k.a. 100%) and used over extended periods of time in large doses has been proven to cause medical side effects.  You should use insect repellant sparingly and if you are pregnant you should consult with your physician.
 
If you also use sunscreen, you should use a low scent/no scent variety.  The perfumes that are put into sunscreen will only attract insects, and worse may attract bears.  No Ad sunscreen which can be found at Wal-Mart is an excellent product for it's ability to protect, be waterproof, and have virtually no odor.  It also happens to be very inexpensive.
 
There are a number of combination products appearing on the market today that act both as sunscreen and as insect repellant.  Off brand is the most popular and these products work moderately well.  At the time of preparing this article, there was no independent data on the effectiveness of these combination products when compared to their stand alone counterparts.  Further, there is no real data on using separate sunscreen and insect repellant at the same time.  You should draw your own conclusions and use what works best for you.

Number eleven, water.  Water is essential when you are hiking.  For every two hours you plan to spend hiking you should carry at least one quart of water.  For a full day you should carry a gallon.  There are a number of solutions for carrying water.  Simple one quart water bottles can be found almost anywhere on the internet or in a store for just a couple of dollars.  Hydration systems, backpacks with a water bladder and a bite valve can also be used.  Camelbak makes a very popular hydration system that holds one-hundred ounces of water (about 3 quarts, 1 cup) that runs anywhere from $60 to $80.  These hydration systems offer many benefits but may complicate your ability to carry a pack.  You also need to keep in mind that your water supply will be the heaviest thing you carry on a day hike.  A gallon of water weighs close to nine pounds!

Number twelve, food.  Food is also essential when you are hiking.  Not only does eating food on the trail help keep your system balanced, it provides a cushion if there is an emergency.  Complex carbohydrates and proteins make the best food to carry.  Dried fruits, jerky, nuts, peanut butter, whole grain mini bagels, prepared energy bars, candy bars with a high protein content (nuts, peanut butter) and crackers make excellent field rations for a day hike.  A self opening single serving can of tuna, a mayo packet, and some creative mixing in a plastic bag can make for a compact and good meal.  Raisins and peanut butter on a bagel is also an excellent energy fix.  You should try to carry at least 2,000 calories worth of food when hiking.  Also, you should double pack your rations in plastic bags and remember to carry out all trash.  If you drop food on the ground by accident you should pick it up and pack it out.