What are your favorite vim/nvim customizations/shortcuts?

One thing I cannot live without: The Emacs-like Scratch buffer. it's quite simple to do in vimscript:

  function Newscratch()
    execute 'tabnew '
    setlocal buftype=nofile
    setlocal bufhidden=hide
    setlocal noswapfile
  endfunction
  com! Ns call Newscratch()

The ones _I_ have made _myself_ to solve _my_ own problems.