Detents & there springs are what I get asked for most of the time . I buy them in 10 pak's because i'm asked a lot for them.
I was asked for a buffer retainer spring the other day & didn't have one & I usually have them , but was out for some reason.
A bolt kit( extractor & spring,ejector & spring ,gas rings) ,spring kit , a lower & upper parts kits .
If some one needs a new trigger , hammer or,disconnector, I usually just get them a trigger system (ALG, Spike's or a custom match trigger system , if they want to spend the money & that's what its all about . Most just want to get back in action.