I don't carry much in the way of backup gear but I do carry a few items that I have found to be quite useful in the past. These are:

1) backup sunglasses (noted in another post).

2) spare reading glasses. I have had a lens pop out of my normal glasses twice when bushwhacking. I was able to find the lens once and could not find it the second time. I don't really need glasses for distance vision but do need them for map and recreational reading.

3) A little key-chain LED light. Actually I use it about as much as I do my headlamp because it is easier for me to use at night. I have a knack for turning on my headlamp pointing the wrong way and have often blasted my night vision as a consequence; I don't have that problem with my Photon light.

4) My "when you absolutely, positively, must get a fire going" kit. For normal lighting chores, I carry Bic mini's, one in my pocket and one in my stove bag. I use the one in the stove bag to light the stove because it saves me having to stand up and get the other one out of my pocket. Yeah, I know, but it is only 0.4 oz. My "absolutely, positively" kit consists of a golf ball-sized wad of paraffin impregnated excelsior, a 1" cube of paraffin impregnated sawdust, two birthday candles and 6 storm matches with striker. All of this is vacuum sealed into a lumpy package about 1" x 1" x 2.5". It is designed for one-time use. I have needed it in the past and it served me well. I think I could get wet rocks burning with it.

5), I carry a small repair kit: thread, needle, duct tape and Thermarest repair kit.

Altogether, my backup stuff weighs about 4 oz. It comforts me to have it along.