If you want "as boring as possible" and "never want to debug" then you probably shouldn't be using Jekyll in the first place; for simple boring use cases all you need is:

  for f in ./posts/*.md; do
      dst=site/$f:r.html
      cat head.html    >$dst
      markdown $f     >>$dst
      cat footer.html >>$dst
  done

Or some variant of that, in your preferred language. There's loads of things you can do wrong in Jekyll even without any plugins, and this applies to most static site generators.

Anyway, I have a list of plugins at [1]; some are as simple as "don't use leading 0 for dates but a space" so it looks nicer (IMHO) but still aligns well, and others are a bit more crazy such as "use Vim's :TOhtml for syntax highlighting because I think Rouge looks horrible".

Stuff like "show all posts with the same tag as the current post" could be done in pure Liquid template too, but this is usually a lot more awkward and a lot slower, and convenience tags like {% warning %}Watch out!{% endwarning %} are completely unnecessary as such, but it's just convenient and nice.

[1]: https://github.com/arp242/arp242.net/tree/master/_plugins