I have played with building the smallest possible, but still having the absolute necessities. What I have found is that, with training, and small knife, small saw, cordage (and dental floss works surprisingly well) and a lighter, you can do much. There are many variables, such as climate, weather, environment and situation (what are you doing there, what happened to put you into a survival situation), but generally these essentials will get you through. Knowledge does not take up room, and does not weigh anything. You always have your brain (or most people do, anyway), and if you prepare that thoroughly, you can make it in most situations. Every tool you add to that increases your chances of survival.

Now, I do have my favorite components to a kit, and there are some that I would try very hard to make sure I take with me if I can. UCO stormproof matches are one of those things, along with 1 or 2 charcoal grill starters ( Ignito ), but cotton balls and petroleum jelly packs very small and works well also. There are several small ferrocerrium rod fire starters, but my favorite I can't find anymore. A disposable lighter is great and small. There are a few small signal mirrors also.

I can go on and on. But then the kit gets big. You have to do the assessment of where you are going and what you can carry.