that's a solid idea, I have some of those beads ...IF I think a rattle would be beneficial on a fly (like a crayfish pattern) in a particular situation, while fishing I'll thread an extra small bead or two on my tippet above a beadhead fly, similar to the way a Carolina Rig works...
...and yes I carry loose beads and conehead cones in my bass fishing gear.
I don't bother adding real rattles.