Slings are the subject of many diverse opinions among operators. In this way, they are kind of like boots; everyone has a favorite.
Single-point slings, while great on the range for dominant and non-dominant shooting, do not control your weapon when you are moving or going hands on with a suspect. If a single-point sling is your preference, check out BlackHawk, CSM Gear, or Daniel Defense.
Quick adjust two-point slings like those from Blue Force Gear and Viking Tactics are rapidly taking over the law enforcement and military market. Tapco offers the Tactical Sling System, which is a crossover between a single- and double-point sling.
Three-point slings give you the most control over your weapon, but they can hang up on the front of a tactical vest. Spec Ops Gear's Mamba or 101 are the class of the three-point sling market.
It is my experience that nearly all of the stock manufacturers offer both mil-spec (1.14-inch) and commercial (1.17-inch) size adjustable stocks. Over the years, I have used stocks from CAA/EMA Tactical, DPMS, Duostock, Lewis Machine and Tool (LMT), Tapco, Vltor, and now Choate.
The biggest change I have seen in stocks is that nearly all AR stocks now have some type of a polymer recoil pad. With a .223 Remington or 5.56mm cartridge there's really not a lot of recoil to reduce. But there is a benefit to these pads. The material keeps the stock from slipping on tactical vests or duty wear.
Some folks will argue that you shouldn't consider vendors that are not DOD approved such as LMT and Vltor. These stocks have been used as part of the military SOPMOD upgrades to the M4. Vltor's IMOD, LMT's SOPMOD, and Choate's AR stock have inline storage for batteries or other small parts. There are also quick release attachments built in that make installation of a sling a snap. Also, the enlarged cheek rest on these stocks gives a comfortable solid cheek weld to the stock.
I know of many folks, myself included, who have and do use non-contract stocks for duty and competition. These stocks have been popular for many years and keep on trucking. My thoughts on stocks are like other parts: I wouldn't buy flea market specials or deals that are too good to beat. Stick with names you know and trust.
When mounting a variable low magnification optic, a red dot, or specialty type scope, a mount with repeatable zero is critical.
Quick release levers are an important feature of any optical mount. They allow you to change optics to meet your mission requirements or remove the sight should it fail so you can go to iron sights. If you use a non-magnifying red dot, I suggest that you be able to co-witness your iron sights at the middle of slightly below middle of the sight's centerline.
I have found the most versatile and durable mounts for duty, competition, and self-defense are mounts from A.R.M.S, American Defense, PRI Mounts, and LaRue Tactical. All four of these manufacturers use quick release levers. American Defense's QD Auto Lock and LaRue's QD Speed Lever both use their own proprietary locking systems to ensure your optic does not come loose. Mounts from either company are easy to use.
A.R.M.S. mounts use QD Throw Levers. While they do not have a lock, these mounts use a cam that itself will lock and secure them to a Picatinny rail. I have yet to see an optic using A.R.M.S. mounts work loose.
One of the newest players to the quick release market is PRI Mounts. PRI's Cantilever Mount uses a self-adjusting spring-loaded throw lever lock. To say the spring lock is snug would be an understatement; you won't rip the scope off of the base. I have mounted a large variable power scope on my SIG 556 using this mount and it has yet to fail me.