BCE goes into some basic details about the BCG, probably the most critical moving part in your AR and provides a very handy list of what spare parts you should have at minimum. Did you catch the part about "at minimum"? That means no less than the minimum but more is certainly better. Based on his list, I need to do better so I am scouring Brownells website but so are a lot of other people apparently because a bunch of stuff is out of stock. I tend to focus on the obvious stuff: moar mags, moar ammo, etc but like I said yesterday, none of that stuff will matter if something breaks inside your AR.
I don't make any pretense of being an AR expert. What I usually tell people is that I am an enthusiast rather than an expert and people like BCE with military experience know a hell of a lot more about the platform than I do so I defer to them..
Anyway, get you some springs and gas rings and assorted gadgets and widgets and gumbeldums that make the AR run, have spare everything and keep your bolt carrier group clean and lubricated.