Recently I added three Ergo Gappers to an Amazon order. They were cheap and I figured they'd look better than the little strips of black plastic I cut off a CD jewel case to plug the trigger guard gap.
Anyway, they fit nice and are softer on the knuckly than metal.
And unlike most accessories, they add almost NO WEIGHT! No kidding, my digital scale reads them at 0.0 oz. In fact it reads two of them at 0.0!
The next lightest accessory I've added is the IWC QD Micro Flush QD Sling MOUNT-N-SLOT which weighs 0.243 oz.
Then the BCM Gunfighter Mod 4 charging handle, 1.2 oz (only 0.1 oz more than a standard Daniel Defense CH).
The Magpul MBUS 2 rear sight is only 1.3 oz...
And the BattleComp Mossie Midnight Mount (for a weapon light) weighs 1.4 oz
The UTG RS10S3 mount for my RDS only weighs 1.8 oz. (I know, hang my head but it does work, hold zero and return to zero after remounting.) (The Bushnell TRS-25 RDS weighs 4.0 oz.)
I know my Noveske QD End Plate is light but I never weighed it. It can't add .5 oz over a standard end plate.
Upgrading from a standard weight carbine buffer to the H buffer adds about 0.9 oz.
Upgrading from the AR-15 carrier to M16 adds 0.5 oz.
Any other light stuff out there?!