I carry two bags as a referee.
At least once a season one of my guys loses one on a poorly lit or snow covered field and I can help out. I usually keep it in a place where it doesn't get in the way.
Of course, last season I was about 8 minutes before kickoff for a HS playoff game and noticed I didn't have my whistle. Umpire offered me his, but I thought better of it and had game management go to the locker room with directions (and a reminder that the game can't start without the R's whistle
).