Most configuration really isn't about the app -- it's about where the app runs, what keys it needs to communicate with third party API's, the db password and username, etc... They're just deployment details -- and there are lots of tools to help manage environment variables -- not the least handy being a simple .env file with all your settings. Simply source the appropriate env before you launch the app in the given env (you could make it part of a launch script, for instance).
env files look like this:
SOMEVAR="somevalue"
ANOTHERVAR="anothervalue"
To source it:
$ source dev.env # or staging.env, or production.env, depending on where you're deploying to
