I carry a backup on duty. Colt Agent .38 spl in an ankle holster. I also carry a Benchmade CQC-7.
On the force continuum wouldn't the pepper spray come before the firearm? Even for non sworn CCW, I think that unless it was a clear cut deadly force situation, the pepper spray should be first.
My plan B in a fight is to fight with every breath in me and every available weapon, and to never give up no matter matter how gravely injured while I still had the means to resist. I think mindset is more important then the layered defense. you can carry backup and alternative weapons in quantity enough that you can't walk, but unless you've made your mind up that you are going to survive and fight to the last you will find them just so much weight.
Plan B is to go home, if it means unarmed combat, a brick, a rock, a 90mm recoiless rifle, it's not the tool used, it's the mindset and will to survive.
Jeff