In a thread below, the idea of humanity vanishing is postulated. ER also points to the classic SF novel "Earth Abides," which postulates most of humanity vanishing. While this is a common theme in SF, the novel handles it with a lot of good analysis and reasoned speculation, not just filling the scene with zombies or something.

The book ends with humanity reverting to a primitive, superstitious state, where humanity has (unfortunately, IMO) spent the vast majority of its history. While this is possible, I submit that civilization and technology at all levels is so prevalent that, even after a disaster, there is a good chance of achieving a level far short of our current civilization but far ahead of primitive civilization, and possibly even ahead of the world of a couple of centuries ago.

What technologies and ideas are around us now that could enhance our lives, yet do not require a large technological civilization to create or maintain?

For sure, something like a ruggedized solar-powered electronic device might last generations with luck, and that's one level. There is enough infrastructure and supplies in the world that a small group of humans could probably live a hundred years just on the leftovers without ever creating much new. A scavenger civilization. I suspect some groups of humans would do just this, which in the long run, would not be too useful.

But other productive achievements, like agriculture, cities, ceramics, the forging of iron, and anything invented in the last couple of thousand years, would certainly be feasible. That alone would take us far beyond the simple tribal things of ten thousand years of our past. Remember, the Industrial Civilization wasn't that long ago, yet the period prior to that was not devoid of technological advancement at the hands of craftsmen instead of factories.

The combination of leftover high-tech and medieval tech would make for an unprecedented situation, and I'd like to see some speculation on this. Imagine taking a smart blacksmith or artisan of the year 1000, and giving them access to the leftovers of our age. Run a Leonardo da Vinci through the Museum of Industry, and I think you might see some interesting activity.