I'm not sure that I understand the question completely. Policy?
Backpacking trips have no single plan. Some have a central commissary where the leader brings breakfasts and dinners and all of the cook gear. That makes it a lot easier for participants since cook gear can get expensive and complicated. Therefore, each participant is more concerned about personal gear, and some people double up with tents to cut down weight even more. If that is the way that a trip is to be organized, then it is advertised that way. Then, a week or two prior to the start, a "trip letter" is sent out, and it has a quick checklist of what is required, versus what is optional, and what shared gear the leader is bringing, carpooling suggestions, etc.
Other group backpack trips are much less organized. Each person brings everything. The leader is just more of an organizer and navigator. Each club kind of has their own traditional way of doing these things. Each club has their own "hard" rules, like no firearms, no illegal drugs, or whatever else.
I think the first lightweight backpacking trip that I led was around 1984, and I just laid out guidelines of what each person should try to do, like have a total load less than twenty pounds. Plus, I offered up a few key pieces of gear, just in case anybody was jammed up. I think we covered 75 miles in three days in Yosemite.
Rules and checklists get a little more important in winter.