Good list. A few more for me:

    * Implementation/header pairs in C++
    * Language REPLs (e.g., Python)
    * Quick calculations in Calc while coding
    * Checking dates on the calendar
    * Magit status
    * Diff buffers (especially diff-buffer-with-file)
    * Listing neighboring files with dired
    * Notes on a code base/task in an Org mode file