Sticking strictly with AR accessories
Elftman Tactical drop in units I have used Geissele before and the elftman units are just better IMHO
https://www.elftactical.com/elf-ar-15-match-drop-in-trigger
Scopes I am a big fan of my Trijicon Accupower 1-8 especially for an AR this should get accurate shots for any 5.56 distance
https://www.trijicon.com/na_en/products/product3.php?pid=RS27-C-1900026
And for handguns or rifles I really like Surefire Weapon Lights
https://www.surefire.com/illumination/weaponlights/rifle-carbine-smg/scoutlightweaponlights.html