Go to Google Takeout… Sign into your account, if not signed in already. Next step create and archive by selecting what data sources you want to download data from (currently 19 different sources).
Depending on the size and amount of data you have stored online with Google, the archiving process can take hours (and even days). The archives are typically broken down into 2GB segments. You will be notified in your Gmail when your data archive is available for download.
This is a good way to determine what data you are storing out there; plus, in the event you opt to change services this data will be available to help smooth the transition.