I’ll keep this short. You should download your Twitter data, Facebook data, and as you probably have that too, your Google data. You never know when you might be banned from using them, even accidentally.
After you’ve saved that data, go to Instagram and Reddit and do the same!
Download your data from Settings->Your Account->Download an archive of your data.
Download your Facebook data from Settings->Privacy->Your Facebook Information->Download your information. I like that they offer HTML and JSON options.
Google Takeout is where you download your Google data. There is a lot there. At the time of writing, it shows 53 products, which includes YouTube, Gmail and Google Photos.
Download your Instagram data from their Privacy and Security page where you will find the request page.
And finally, Reddit. You can download your data from their data-request page.
Keep that data safe. Don’t leave it in your download directory. It potentially has lots of private information you won’t want to be shared with anyone who uses your computer.
Google lets you schedule up to 6 data downloads per year, but it might be worth setting a calendar reminder to do this at least once a year. Store your downloads in dated directories to make it easy to keep track of when they were downloaded.