I've kicked around just about every configuration of Remington 870 there is over the years. Different stocks, lights, slings, extensions, sidesaddles. I've owned 870 police, wingmasters, express,and "tactical" models. Some I've sold and some I've kept. I think I'm down to 7 at the moment.
This is where I've arrived and the one that stays handy for "social" engagements.
It's a police trade in wingmaster 18" that came from Kings Firearms. It had Orange Speedfeed stocks on it when I bought it.
I swapped them out for Magpul. It is setup with a short LOP. I'm 5'11" with monkey arms but I shoot a short LOP on everything. It's faster to the shoulder.
It has a Wilson Combat +1 extension. This gives me 5+1 in the tube and keeps the handling quick. Too many rounds too far out in front of your hands is heavier and thus slower to drive. I'm not going to war here or shooting a 3 gun stage where I need a lead hose. I need to be able to solve problems at speed.
Esstac Velcro card on the gun for +6 on the side. There are several others Velcro'd to the side of the gun safe if I need to grab and go (unlikely). I keep all my cards set up with 4 00 buck oriented up and two slugs out front oriented down. I load buck under into the tube or slug over into the chamber as needed.
Streamlight TL Racker is the best light system for a shotgun I've run. Much better than the Surefire that I replaced with it. Easy to activate on purpose. Hard to activate on accident. Smaller, slimmer, and lighter.
Suarez RMR mount drilled and tapped to receiver. Holosun 507 mounted. The ⭕ reticle is perfect for shotgun applications. In my testing, in this gun, the reticle is the pattern with Federal Flite Control 00 out to 30 yards. At across the bedroom distances the reticle and pattern are the size of the T box.
I have QD socket sling points at the wrist and end of mag tube. I have a sling hanging near the shotgun. But I do not keep one on it.