What type of outdoor pack should I buy for a 1 month hiking/camping trip? How big should it be (50L, 80L)? Are there any special features I should especially look for (pockets, types of material)? What are the best brands (the only brand I really know of is the North Face)? I am looking for something not too expensive but that I can use on future trips as well. Any advice would be greatly appreciated. Thanks 