First decision is what are the lowest temperatures you think you'll be backpacking in? Then decide how good you are at erecting a dry tent (do you need to go synthetic or down). Then visit Campmor or Sierra Trading Post online and get a name brand bag.
In this world of sin and sorrow there is always something to be thankful for; as for me, I rejoice that I am not a Republican.
- H. L. Mencken