I want to give my sister my old iPad without deleting the videos and music I've put on the device. What do I need to do to deactivate it from my iTunes account without deleting the video and music content?
Once she decides to sync the device once, the contents will still be removed. Your sister won't be able to back up the videos and music or sync it to her iCloud, but it should keep playing all the media for months to come. If she erases it or syncs it with a new computer - she can return it to you for a reload or just start fresh with her songs at that point.
To remove your accounts, open the Settings App:
Sign out of social media - Twitter, Facebook, Flickr, Vimeo
She should be fine adding her Apple ID and just will want to watch for prompts that indicate if she will ever wipe your videos and music. Depending on what you choose, you might just erase all content and settings and copy the Music and Videos to a $50 hard drive or large USB drive so she can incorporate them in her iTunes library rather than have you surgically remove things. The out of box experience does guide a new user to understand what accounts and settings she can opt in and out of.
Here are the official instructions how to do that.
Removing an associated device or computer from an Apple ID