Here's the way we handle things - short and sweet...
Your Scout Book, NoteBook, Pen or Pencil is part of your "being prepared" gear....Uniform, Scout Book, Notebook, Pen/Pencil, etc...
These are to be brought to every Scouting event/activity unless otherwise notified by your SPL or an adult leader - Every boy, every time reguardless of rank or age is required to have his Scout Book available at all Scouting activities. SO - This could mean - if you're not told ahead of time, to bring it to the Troop Swim Party (for example) then you should very well have it with you....."Being prepared for any ole' thing" comes to mind...
Brad G
SM BSA T23
OKC