jon-
I would have to disagree with you. Aeons ago, I built a custom magmount CB antenna. The stick is made from an old fiberglass fishing rod, about 1/4" in diameter, probably four and a half or five feet in length. And it breaks down in two with a metal ferrule in the middle. On that, I wound 1/4 wavelength of maybe 24g copper wire, experimenting to get the best spacing I could to fit the entire rod length. (Hey, it was what I had at hand.) The base was simply the capacitive coupling to the car roof, courtesy of some magnatron magnets, since we didn't have rare earth in those days. SWR? About 1:1.1 from the start, signal reports always were tops.
Now, what's that got to do with backpacks? Well, the same fiberglass rod could extend UP from the backpack. And a second rod could extend DOWN as the other half of a dipole, instead of the magmount base.
Ought to be a piece of cake, and an easy project for teaching kids. With CB's limited output power, proximity and rf safety should be no issue. Easy enough, cheap enough, to have a go at it. Thin wood dowels or bamboo, or old fishing poles, or those 4' long driveway marker posts, all make cheap antenna rods, and 24g wire is more than adequate for the power.
Or am I missing something here?