Right-click a bat with an empty bucket to capture it (if you can!) and get the Bat in a Bucket. Right-click to release the captured bat, causing the outline of all entities around you to be visible for a moment.
Right-click on a banner or beacon while sneaking with a compass to bind the compass to the banner or beacon's location.
Moonstones help you locate a specific block co-ordinate across dimensions or aid in aligning builds.