Anything on your device that is part of a Google account should be automatically synced with the Google cloud--that is, assuming it is set to sync. You can make sure by going to Settings/Accounts-Google/[your Google account], and making sure everything is checked. After you do the factory reset and then log back into your Google account with your device, items that have been synced with your Google account should be automatically restored.
You won't lose any contacts as long as they are synced from some cloud account (i.e., Google, Yahoo, Facebook). The main thing to be aware of is that if you're on a phone, you need to be aware of any contacts that are saved to the Phone Account. These contacts do not get synced with Google, and probably not with any other cloud account.
If you go to Settings/Backup & Restore, there's a setting for "Backup My Data"--if checked, a lot of your settings and account data will get backed up to your Google account, and restored after you do your factory reset. All of your apps from Google Play should also automatically download and install, but apps from other sources (like Amazon Appstore) will have to be reinstalled manually. Save game progress may or may not be restored--I think it depends on the game.
Photos and videos that you saved locally will not necessarily be restored unless they were automatically backed up to Google+, so make sure you save them somewhere first.
Posted via Android Central App