The troop buys pizza for all the participants. The adults bring in literature for the boys with camps, activities, etc. We don't start to narrow down ideas till the next day. We list things we like to do and things we might like to try. Boys come up with the ideas.
Leaders are moderators and can provided idea sources.
Then the next day we start to actually work out the schedule. We list themes we'd like that the ideas listed the night before can fit into. We then begin to match themes with months. Once the themes and major activities are matched up, the remaining weekly planning becomes a cinch. We break it up every so often with games and team building exercises.