You say that the group will provide shelter. Does that mean that you will sleep in tents or will you be in a bunkhouse? Clothing would vary a lot if you are coming back to a bunkhouse. If you have to lug all of your clothes along with you for miles on your back you will be sorry that you took so much. You should get more specifics from the group before you leave. All of the groups that I have been with have provide very detailed information on what you need.