Along with the preparation part, your mental attitude is what will get you through. You need to be 100% confident in the items you include. Don't skimp on quality thinking that you'll probably never need it anyway. It's like CCW. If you need it, you really need it. Buy good quality and practice using the stuff in your kit in the dark, when you are wet, cold, tired and out of breath.
Every so often, I do a bare-bones solo camping trip where I experiment with bow-and-drill firemaking, field-expedient shelters, catching and cooking game, etc. I'm confident that I could survive several weeks, if not longer, with nothing other than what's in my daypack. I could set up camp like Grizzly Adams with what's in my truck.
Survival kits are highly personal, reflecting the beliefs of the person who made it or carries it. I like redundancy for the items I consider essential which is why I carry more than one knife and more than one signaling device. I also like the Mg fire starter since it's what I was issued in my A.L.S.E. vest in the Army. I'm very familiar with it and confident in my ability to make it work.
I'll admit that the fishing kit is of questionable utility but it takes up about as much space as a matchbook so I keep it in. I also carry a cyalume lightstick and a trioxane fuel tab that I forgot to mention.
I'll second the energy bar idea. My car kit has two MREs but they're too bulky for a day pack.