Here is a terrific hidden InDesign keyboard shortcut. Say you’ve got a bunch of InDesign files open that you’ve been jumping between, and you need to save them all before stepping out for lunch. Use InDesign’s Save All command to save all your open documents.
Source: This tip was one of Scott Kelby’s 10 Quick InDesign Tips in an episode of Layers TV earlier this year. David Blatner has also covered this trick at InDesign Secrets.