Usually what is included in a Lower Parts Kit. Most packaged LPKs also include a pistol grip and its fasteners.
Slick skeletonized lower from Aero Precision. This is hands down the coolest lower I've ever seen and would love to own!
Battle Arms Development Ambi Safety Selector (BAD-ASS) in different colors
Tennessee Arms Company complete AR lower receiver with standard equipment
Learn how to quickly build an lower receiver with pictures, tricks I learned the hard way, and recommendations of the best parts and upgrades.
How to Build an Lower Receiver: Ultimate Visual Guide - Pew Pew Tactical