What skills do you think would be useful for bartering in an economic collapse type of situation?

I'm thinking of a situation similar to when Soviet Union collapsed. Some people lost their regular jobs, and many others were paid very little in those jobs. One way to get more money was to get a different job that paid better; another thing some people did was to privately provide some kind of services (such as plumbing or doctor-on-call). I'm wondering what kind of services would be easier to monetize (I use "monetize" figuratively since paper currency may not be the most valuable thing in a situation like that).

One recommendation I've heard was to be a handyman, i.e. perform simple household repairs. This is convenient in that it requires relatively little skill. The flip side is, there may not be much demand (since almost anyone can do simple things by themselves, especially if money is tight) and a lot of competition (since anyone can offer these services). At the other extreme are doctors. This is a service relatively few people can offer (although I've read the discussion in the other thread about how even these few may be too many). But the real problem (for me) is, I cannot be a doctor as a hobby; it requires too much training to just do it on the side.

I'm wondering whether there is a middle ground, i.e. something that is simple enough that I can learn it as a hobby, but difficult enough that not just anyone can do the same. Ferfal's book about crisis in Argentina suggests that for those who spoke English, it was easy to get a job as telemarketers. This is the kind of suggestion I'm looking for: it's easy enough (and maybe even fun) to learn a foreign language in a couple of years, but it's not so easy that anyone can learn it in a week after the economy collapses. But I'm not sure how to adapt it to the US. Most people here already speak English, and it's not quite clear what other language to learn. Of course, I'm interested in suggestions other than learning foreign languages.