Other question concentrate on most valuable goods but most of good listed would involve local trade - for example alcohol can be easily produced with modern knowledge anywhere (see Prohibition in the USA). In similar way the livestock etc. The only things in answers to that question I saw for long-term traded goods would be salt and spices which cannot be produced locally without modern infrastructure.
However I'm more interested with goods which would form a basis for new continental trade networks, like copper and zinc (in the Bronze Age), famous Silk Road and less famous Amber Road (I've seen some speculating about Jet Road being a source of caps being universal currency in Fallout).
What goods would start traveling across Europe or across America when society collapses and starts rebuilding at level of city-states (with larger political entity here and there)?
EDIT For purpose of this question please consider standard nuclear apocalypse with radiation glowing green and roaming bands of mutants.
EDIT 2 To clarify I'm looking for good which is a) valuable in such setting and b) decentralized. I don't think that ammunition or guns would be found in much larger quantity in east coast than west coast to make the trade route. On the other hand I don't think black pepper can be easily grown in North Canada.