This started off as a stock Colt LE6920 a couple of years ago, wanted known quality/reliability as my baseline.
Now it has a BCM 16" LW middy upper (lighter bbl, smoother recoil impulse, longer hand guard, less wear/tear on parts)
AIM V2 Nitride BCG (less coefficient of friction than a std phosphate bcg, surface treatment that can't peel or flake off like some coatings)
Precision Armament AFAB (reduces felt recoil by 55%, also reduces muzzle rise w/little more flash/concussion than a std A2)
Magpul MOE fore end (inexpensive, lightweight)
Magpul K2 pistol grip (more vertical angle, holds lube & spare batteries for the Surefire M600U & Trijicon MRO)
Magpul MBUS Gen 2 rear sight (lightweight, inexpensive, relatively durable)
MFT Minimalist Stock (lightweight, inexpensive, handles well, QD sling swivel socket)
Surefire M600U on a Magpul MOE scout mount (tried lots of other lights, all were lacking something, finally did the 'buy once, cry once' route w/the excellent & lightweight M600U)
Trijicon MRO (lightweight, long battery life, rugged, excellent FOV through the optic when compared to the Aimpoint Micros and less expensive)
Odin Works enlarged mag release (for more positive reloads, not visible)
Redi-Mag's Redi-Catch & Redi-Release (together they function the same as the Magpul BAD lever, but more reliably & w/o taking up space in the trigger guard)
MFT Torch nav light (for getting from A to B at night w/o broadcasting your location or ruining your night vision, not visible on the right side of the hand guard)
Magpul MS1 sling w/QD sling swivels (relatively light weight, quick-adjust, easily removable for cleaning and such):
Tomac