A good sleeping bag is one of the most important investments you will make as a scout, and critical to your comfort on camping trips. A good bag will last for years, so you should shop and choose carefully when buying one.
When picking a sleeping bag, be sure to look only at "stuffable" styles. The thick rectangular style that needs to be rolled up is only suitable for car camping or very short backpacking trips since these bags are difficult to affix to a pack and take up a large amount of space. This makes movement in tight spaces difficult and snagging the bag on branches probable. A stuffable bag is meant to be jammed randomly into a nylon stuffsack or the sleeping bag compartment of a pack, and should always be stored unstuffed or very loosely stuffed (usually two sacks are supplied with the bag, one very large and the other small for backpacking) when you are not actually backpacking.
The two basic sleeping bag groups are synthetic-filled and down-filled. Each has advantages and disadvantages and is available in a variety of shapes and sizes, but many experienced backpackers and mountaineers have both. For backpacking purposes, most people prefer a mummy or modified mummy shape which fits the body closely and therefore traps heat more effectively. Some people prefer roomier box or rectangular shapes, but these will take up more space and weigh more. Try to buy a bag that is comfort rated down to at least 20 degrees (the comfort ratings are often optimistic, and it can easily go below freezing on an overnight, even in summer). Bags rated at 0 degrees to 10 degrees are often too warm for summer use, but essential for snow camping or mountaineering.
Synthetic-filled bags are normally rip-stop nylon shells filled with polyester fibers. The best synthetic fibers are actually hollow, and have wicking characteristics as well. Some of the best-known brand names for insulation fibers are Dupont's Hollofil® and 3M’s Polarguard 3D®. Both are excellent. Synthetic bags have the advantage of performing well even when wet and are reasonably priced. They weigh somewhat more than down bags and don’t pack as small, but require less stringent care and are generally a good choice for the damp Northwest.
Down bags are often the choice of mountaineers and people who camp at higher altitudes. They cost considerably more, but weigh less and pack very small. The styles will often be exactly the same as the synthetic bags for a given company. If you choose a down bag as your main sleeping bag, you need to be sure your tent is seam-sealed and leak proof, including the floor, and take precautions to keep your bag dry in your pack as well. Down requires extra care to maintain its loft, or heat-insulating qualities, and should never be left stuffed tight longer than necessary. Down insulation comes in various grades, usually designated by a number (600 or 800 are common, with the higher number indicating higher insulating ability by weight) and if properly cared for can last for many years.
For most all-around summer and fall backpacking the 20 degree synthetic bag is a good choice. Remember to fluff the bag up before you use it regardless of which type you have. You can always "warm up" a bag by putting on a set of long underwear before you get in, and liners or inner bags are available that can extend the comfort range of a light bag for 3 or 4 season use. Manufacturers offer a choice of left or right hand zippers (right-handed people usually reach across their body to zip or unzip their bag and prefer a "left" zip) but in reality you can adjust to either. There are often more "right" zip bags available at closeout prices. "Regular" bags are usually good for people up to 6 feet in height, and "Long" bags usually good for those up to 6'6".
As usual, the flagship REI store is a good place to start when shopping, in order to get an idea of what is available in different price ranges. The Internet is a good place to check after you have done some basic research; some useful sites are www.sierratradingpost.com, www.rei.com, www.backcountrystore.com, and www.campmor.com. Many offer significant discounts on new merchandise from the previous season and on closeouts. REI's online discount outlet is always worth checking out at www.rei-outlet.com. A good sleeping pad, either closed-cell foam or inflatable/foam, is essential, especially if you plan to camp on snow. The classic Thermarest® pads are not cheap, but will last a lifetime if cared for properly and are extremely comfortable and easy to pack.
Be sure to take your bag out of your stuffsack or pack immediately after returning from a hike. Unzip the bag and put it in the dryer on low heat for about fifteen minutes (or fluff it vigorously and let it sit exposed to the sun both inside and out), then let it air out in the house for another day or two before putting it in the big storage sack. Some people prefer to hang their bags in the closet, which is probably even better. A note on junior-sized or short bags: they aren't generally a good investment unless a scout is quite small and there are other siblings coming along that can use the bag later. Most kids of eleven or so will outgrow a junior bag in a year or two.