Simple Calendar Pro, Aegis, Feeder, and NewPipe are a few examples of open source apps available through F-Droid that allow you to easily export your data.
When you sporadically decide to back your stuff up it might be a good idea to include them with everything else.
You can also use these files to transfer data between apps. If you are using Feeder as an RSS reader on your phone you can transfer the OPML file to GFeeds on your computer.
AntennaPod (podcast app) is another great example, offering to either only backup the subscriptions or the whole database with listening history, statistics and what so ever.
Antennapod’s implementation of this is so nice. My Antennopod DB dumps have survived 5 years, multiple device transitions and almost 1500 hours of podcast listening.
Some other apps that I use that do a good job at dumbing/restoring their data: