I think medical treatment is the biggest obstacle to overcome in a SHTF scenario. You can stock all the supplies and ammo you want, but a case of pneumonia or an infected wound, can be a real dealbreaker on survival. Food wise , I think we would be ok. We raise a big garden, do a lot of canning, have started a modest supply of staples, etc.. I found it interesting that in the book Patriots, they mentioned dental hygiene several times. I hadn't really thought of it in "prepper" terms, even though I have first hand knowledge that an infection from a bad tooth, can in fact, eventually be fatal. In addition to stocking supplies , I have added trips to the dentist, an attempt to shed a few pounds, and a feeble attempt to quit smoking, to my list of prep items.
I agree wholeheartedly with the above quote. As for immediate survival, my biggest obstacle is assembling my immediate family. This will take about 30 miles of driving and is my most vulnerable period in any such scenario. Once that is accomplished I feel that chances of survival become pretty good assuming that there is not heavy fallout directly in our area. I would have 4+ adults together with plenty of supplies in a fairly safe and inaccessible area. Even fallout is survivable, but will make life much much more difficult for several weeks. In the long term, medical care is the biggest challenge as per the above quote.