I have a Rock River Arms AR15 and am wondering what to do next. It is a CAR A4 with ARMS 40L rear sight, vortex flash hider, sure fire tac. light, detach. carry handle, and CTK P3 mono grip.
A sling is a nice addition. A nice sling (i.e. Turner) can even improve your shooting if you use it correctly. Although a shooting-aid sling wouldn't be necessary if it's purely a CQB tool or if you wanna use the monogrip. A Turner sling and monogrip really aren't compatible, but a VTAC or something is nice to keep the weapon ready.
If you're a serious shooter, A sling should be one of the first accessories you put on your rifle. It allows retention of the weapon while you are free to use both hands for something else.
Other than that, yea an optic sounds good.
I've heard too many stories about Eotechs (affectionately known as 'Eoturds' by some) having leaky batteries, shutting off when they need it, and broken switches to really trust Eotechs. However, having held a friend's carbine with an Eotech, I must say i *really* love the HUD view an Eotech gives.
Be sure to look in to Aimpoints too--I think their battery life and durability is superior. An Aimpoint M4 is pretty much bullet proof with like, 80,000 hours of operation per battery and something like 100 foot submersible water rating etc.
my buddy has an eotech and i think its great, but Some flip up sights would probably be advisable, it doesn't matter how cool your gun looks if the battery is dead and you can't hit anything, that being said when its in my budget I am buying an eotech for my AR