I recently found out someone didn't know this.
Say you want to quickly change multiple pieces of clothing (swapping craft or adventure classes suddenly makes you nude). There are two ways to be able to do this quickly. The SLOW method is to select each piece individually and drag and drop it in the location in your equipment window.
Option 1: place each complete set of clothing in it's own backpack pouch. Set the backpack pouch inventory window to list view. Click on the bottom item, hold down shift key and click on the top item. This selects all of the items in between as well. Then drag all of them to a slot in your equipment window.
Option 2: If you prefer to use graphic view instead of list view, hold down the ctrl key as you click on the items you want to equip. That selects each item individually. Then drag all of them to a slot in your equipment window.