I have not put thought into carrying a full-zip bag incase of leg injury. My 3 season bag has a half zip.
I carry a small knife (Buck Mini, no longer made) that has about a 2" non-serrated blade. As long as it is sharp, I don't see the need for a longer blade.
I do carry clothing for extreme temps. I do almost all of my camping in Minnesota, where. What does this amount to? I now always take at least hat, gloves and a Montbell Thermawrap UL as puffy insulation for 3 season temps. Temps can plunge into the 30s easily in the evenings, especially in northern MN. As for winter, I always have a down jacket with me, even though I may never need it, I may use it.
I'm not sure how to gauge the strength of my 3+ season shelter systems. I have a poncho tarp that I have yet to use, a 9x5 sil tarp that I have not had a real chance to use in inclement conditions and a TarpTent Double Rainbow. When solo, either of the tarps will go, and I plan on adding a bivy sack soon (either a MLD or TiGoat). Whenever I am with another person and there is no snow on the ground, the DR goes no matter what. It is quite light for two people and it quite strong, as some wind tests posted on this forum show. With another person, I guess the DR is probably overkill versus what is available. In winter, I recently purchased an ID MK1 XL; its first serious trip is going to be a 2-week snowshoe trek in northern MN in January. I went for it because I wanted a shelter that I knew could handle strong winds off Lake Superior and deal with a heavy snowfall (caused my lake-effect snowstorms). In that case, it is probably overkill, and a pyramid shelter would be fine. (I am currently putting serious thought into an MLD Duomid for future trips, but I cannot justify purchasing another shelter and/or returning the MK1). So yes, I probably take a more robust shelter.
My first aid kit and repair kit weighs in at 3.7 oz. It has duct tape around a straw, strong thread, needle and seam grip. The FAK allows me to deal with blisters, bleeding, the runs, pain. I do not carry SAM splits, but I believe if the need arose, I could fashion something out of foam pad and rope.