I will also add that I'm trying to grow cinnamon, vanilla, pepper, ginger, and a few other herb/spice types.
Additionally - I live next to (well, very close to next to) a state forest... I don't have time to go out chopping wood - by default, I would be trading food (or anything else, really) for someone else to spend the day out chopping - especially if they had a modicum of understanding of land management, not chopping down every single tree, allowing regrowth, and making sure that others using the same resource understood that very important principle. We would not want to copy Easter Island, after all.
Let's face it - potash would be profitable for those who know how to extract and purify it, and what it's good for.
If and when the lights go out, such knowledge, when applied, can give you ideas of what you can trade.