Yes, you can manually backup Outlook's data.
Go to the /Users/your_account/Documents/Microsoft User Data/Office 2011 Identities/ folder.
Backup the folder within that named Main Identity. That's everything. Your emails, account settings, contacts, etc. To restore, just put it back in the same place (same path structure) and Outlook will find it.
This tool (Outlook Mac Archive Tool) offers an automated way to archive mail (and calendar items) to your local hard drive or storage. It maintains your folder structure and you can schedule it to regularly run based on criteria like: archive mail older than X days.
It also supports optionally archiving to the cloud from Outlook which moves your mail in to a cloud mail account like GMail for safe keeping. This keeps your mail backed up, yet is still accessible and searchable.