Go to Home Depot and get one of the little canvas tool bags to hold everything. Mine's about four inches square by about twelve inches long. Here's what I keep in mine (I've just gotten into black rifles and have a XCR so haven't added anything specific for it yet).

Good screw driver kit
Set of drift pin punches
Small hammer with brass and plastic tips
Small tube of oil
Small bottle of Hoppe's #9
Small box of gun swabs (about 1 inch square)
Boresnakes for 9/.38/.40.45/.22
Spare grip screws

I work on all my Sigs and haven't had occasion to need any spare springs, etc. (yet). I don't do complete detail strips at the range, so leave the spare roll pins, etc. at home.

Reading the above, I'm going to take the advice offered and add a take-down cleaning rod for the XCR. It's supposed to have a bullet-proof bolt and extractor based heavily on the AK so I'm not sure what other spare parts might be needed for it - although if you take off the grip in the field and lose the little spring for the safety I'm not sure what the effect would be. The spring powers the safety detent and for sure it wouldn't stay in the Safe position, but I don't know if recoil would knock it out of Fire position while shooting. I'm not inclined to experiment.

By the way, the same canvas bag easily holds a dozen 30rd magazines with room for more.