Armor and Weapons: Damage reducing armor, Archery rules, Handedness rules, Encumbrance, Two-Weapon Combat, Arrows, and Ammo. Deceptive Equipment (the deceptive equipment was good for one adventure and then went in the dust bin).
Mini-games: The Indiana Jones-like chase rules. Largely non-lethal, good for getting the mechanics of die rolls down and escaping combat while still getting the sense of risk.
Quick unarmed combat for AD&D and B/X. Avoids grappling, etc.
Standard Character Sheet for AD&D, this is my classic AD&D character sheet available which incorporates Unearthed Arcana. It is available at DriveThruRPG.
Professional Skills and NPC Skills, this is my book Zero to Hero: Uncommon Commoners, also available at DriveThruRPG.