Hey Archman, welcome to Gunnutz.
My XCR has a Dlask adapter, Magpul CTR w/ riser & "enhanced" pad. Magpul rail covers @ 6 & 9 <--only when needed, and a Ergo grip. Furniture in od green.
Optics are PEPR qd mount, Vortex Viper PST 1-4, Vortex zoom lever. No buis.
Vickers sling w/ qd front and rear.
The Magpul butt pad was a letdown, but the Vortex zoom lever and the Vickers sling are must haves.
Now technically you asked "for an XCR" not
on an XCR. If you're looking
for accessories, to buy, see the list above.
Probably cheaper to buy new though.
Oh, I have a sh!t ton of mags too. Those aren't for sale.
* If you'll be shooting a lot of surplus, see if you have the (optional) x39 hd hammer spring. You won't need it until you need it. Wolverine carries them.