Normally Drupal sorts the “Select an existing field” select list by the field types. Here’s an example of what this looks like:

This looks good at first glance, but often it’s hard to quickly find the field you want to reuse. Most of the time you’re scanning the list for the name (label) of the field you want to reuse. Wouldn’t it make more sense to put the field label at the beginning and sort by that? I thought it would, so I made it happen with a quick userscript.