If you've read other articles on the subject, you should have all of the gear necessary to have a successful outdoor adventure trip. I have been remiss on a very important topic, however: how to actually pack your things! While this may seem obvious, in reality a large amount of space is wasted if it is not done properly. Further, people may begin to skimp on important items if they find them running running out of space. Never fear, below I will outline how to pack for efficiency, weight distribution, and by order of importance on the trail.
Think of your pack as being in layers. We'll start from the bottom up, and end right at the point at which you zip the pack. The bottom layer is where we are going to put clothes, and later soiled clothes. You should first put a small trash bag in the bottom of the pack for later. This will become our "laundry bag." Why plastic? You may be surprised to find that some of your clothes will get quite wet with perspiration. Getting them to completely dry will be difficult, and getting the smell out will require a washing machine. Placing them in a sealed environment will keep your pack much more fresh and dry.
The next layer will be your clean clothes. Instead of folding them like you normally would, you will need to lay them out flat on the floor and slowly and carefully roll them up. You will want your shirts to be no more than thin taquito-like rolls, and your pants should be like long burritos. This method of rolling will save you space, as you will see once you start placing them in your pack. The shape's design lends itself to the contours of a pack and will leave you much more room at the top for your equipment.
The next layer is your food. You will want to pack your trail food more towards the back, particularly if you have flat packs of them. I have recommended in earlier articles to go to surplus stores for military meals ready to eat (MRE's), in which case you'll have flat slabs of food that make a good base for the pack. If you find this too hard, place a thin layer of clothes in between your back and the food so you have a softer, but still firm backrest.
Above the food you should have your less essential equipment. Fire starting tools, water purification, things like this are useful, but rarely necessitate immediate deployment. Try several different methods of fitting things in until you find out which things will fit like a puzzle. Also, if there are any brand new items, make sure you take them out of the packaging. It can lead to litter and will cause you to lose space.
At the very top of the pack is where you want your safety equipment and snacks. Your whistles, flares if you keep them, radios, and first aid kit should be some of the first things you reach in and grab if necessary. Should someone be bitten by a snake or trip and hurt their ankle, you do not want to have to unload all of your gear to access a wrap or anti-venom kit. The snacks part is left for last so if you start to feel hungry and you do not have any food on you, you will not have to stop the entire group to fill up.
If you've been paying attention, you'll notice I left one important item out: water. Drinking water will generally go in one of two places. The first will be in a canteen or bottle in a holder on your backpack or on your person. The second is in a hydration system (like a Camelback) that will fit either in a pouch in your pack or in a smaller, thinner backpack you'll wear out your main one. Since water is your most important asset, it should have a special location. Water is your second pack, not part of your first one.
If you're going on an outdoor adventure trip for the first time, consider hiring or at least contacting an adventure guide company. Especially for Grand Canyon rim to rim trips, a tour guide company can give you the ins and outs and ensure you have a great trip. Good luck, and stay safe!