Being self sufficient is a damned tall order - even the minimal impact arcologies made with the best tech 2030 had to offer couldn't do it. Villages and towns cobbled together in the wake of a disaster - good luck.
Its really hard to generalize about trade routes - so much depends on the area, the needs of the people, alien levels, and the like. If I had to make categories, hmm - lets go for four types. Protected, Directed, Casual, Smuggling.
Protected caravans carry all the high priority things with immediate value. Yes, surgical tools and spare parts are always needed - but if you stole a bunch of them, it would be hard to use them yourself or sell them to the very next person you saw. Food and munitions, on the other hand, are valuable to anyone at any time. As such, these caravans travel only rarely, on previously scouted routes, and only if they have acquired a large number of guards to keep it safe. They aren't always very good guards - if you want some travel in your life, they'll accept just about anyone really, so feel free to sign up - but there will be a lot of them.
Directed caravans are for important stuff that doesn't need such heavy escort. Might have some guards, but most of the defense is just the operators own weapons, vigilance, and deals with the local raiders. Like a protected caravan, they tend to have a set destination.
Casual caravans are your wandering traders, making a general circuit, or speculating on rumors and coded radio transmissions.
Smuggling in this context doesn't quite mean illegal stuff, it just means small scale and using a combination of mobility and wits to make it through. A group of thirty guys, eight vehicles, and ten thousand rounds of ammunition doesn't happen every week, or even every month. Sending it via different method might not make it. So if you absolutely need to deliver bullets, get four people, and give them each a pack containing two hundred rounds. They split up and travel the back ways. Its pretty hard to notice them, and even if one or two get caught, most of the delivery gets through. Not the safest method, but usually the fastest, and at times, that means the best.