You're going to need to incorporate a factor related to standard of living. For example, a big fraction of our electronic equipment is imported, including stuff like TVs that might be considered optional, but also including much of our computer and communication infrastructure. Bringing that back to our shores would be expensive. Cars and clothing are also largely imported. We COULD make this stuff ourselves--and did up until maybe 20 years ago--but it would be quite a change if we closed the borders...

From a subsistence level, the U.S. still has tremendous resources and could easily be self-sustaining. I'm not so sure about Europe, but then it depends on where the eastern edge of "Europe" is defined.