Since you can't cash out your credit, here are my suggestions:
[url=http://www.dsarms.com/item-detail.cfm?ID=CP25&storeid=1&image=]Trijicon 3-Dot Night Sights for M16/AR15, front and rear[/url]
I have a set of these on my A1 carbine, it works very well.
[url=http://www.dsarms.com/item-detail.cfm?ID=116&storeid=1&image=magar30.gif]English 30-round Steel Mags[/url]
Yeah, I know you can get them cheaper here on EE, but if you have to use up the credit at DSA...
[url=http://www.dsarms.com/item-detail.cfm?ID=823&storeid=1&image=magpull.gif]Mag-Pull (pkg. of 3)[/url]
I would have mentioned the various rail accessory fore-ends, but none of them fit your mid-length carbine.
Just curious, why the A2 stock, unless you have long arms or do a lot of prone target shooting? I think the A1 stock (called the C1 by Cavalry Arms) is a better choice for a carbine.
Also, do you have a flattop upper?