As the title of the book suggests, maintaining your body temperature is the highest priority. Shelter is good for preventing both hypo and hyperthermia, thus the redundancy. Personally, I like to spread the redundancy amongst different parts of my packing. I've put disposable ponchos in my fanny pack and my wife's purse, 2 pocket shelters and 2 lightweight space blankets in the small section of my PSK, a tube tent in the big section, and some garbage bags in the first aid kit. If I only get one piece of luggage out of the plane, then I've got some shelter.

I ordered an assortment of fresnel lenses from here:

http://www.3dlens.com/

It's a taiwan company, so shipping is rather slow- I haven't gotten it yet, but it's only been a week. I ordered 2 each of the various thinner sizes. I'll decide which to pack when I get it. One nice thing about fresnel lenses is you can easily cut it down to size if it's too big. I'll cut one to the size of my PSK and put it on the bottom, and another one to the size of my 3x5 signal mirror and store it with that. An extra CC size will go in my wallet. It seems like a lot, but they don't take much space. If it took much space I wouldn't bother with redundancy for a fire-method that sucks when you need it- If it's sunny out, who the heck needs a fire?