Are there any rules for combining different clothing/armor for providing AC? For example, can an adventurer wear full plate and bracers and get the AC bonus from both? Can an adventurer wear a Cloak of Protection over plate? Can an adventurer wear a helm or crown and also plate armor, or does the plate armor include a mandatory helmet and preclude any other headwear? 

I understand that ultimately this is up to the DM and what makes sense, but I would appreciate if there were some rules I could use as a foundation for rulings.