The best way to prepare for future evolutionary challenges is to stockpile genetic diversity. More genetic diversity means both less of a chance of the entire population being vulnerable in the same way to a new threat, and better chances to reach new local maximas that are two or three hops through rough terrain in the evolutionary search space.

Continually applying harsh selection criteria just homogenizes a population to a local maxima and leaves them vulnerable to future change.

How about... wearing clothes? Cooking food?

Not really. This is a naive interpretation of Darwinism. If anything, humans have become more genetically fit by mixing various formerly isolated populations together. Which is very much a consequence of global civilization.

By far the largest problem of any genetic pool (animals, plants, whatever) is not having enough genetic diversity in it. See: Cavendish bananas, the Tasmanian devil.

Ok, well if you want to do your part to contribute to the genetic excellence of the human race, don't use medicine. If you get an infection, instead of using antibiotics, just let it kill you. Don't get glasses, just let your bad vision get you killed. How far do you want to take this? I'm sure you can increase the immunities of future humans by drinking out of puddles like dogs do. It doesn't seem to make dogs sick, presumably because all the dogs in the past with weaker immune systems died, probably with a lot of suffering.

I doubt you do any of these things, because you aren't willing to accept the low chance of survival-to-adulthood that typical wild animals have. It may keep their genetics in tip top shape, but is that really what you want?