Personally if it were me I would do one of three things and I have done both.
1. Nowadays someone in the house probably takes medication. I save all pill bottles, and they come in various sizes, and put parts in these and put a lable on the bottle
indicating the rifle, the part and the date. I have one spot in my shop were all these are placed.
2. You can remove the buttplate, an if the part is not too big, use a drill bit (I like the foredoms, and drill hole in the buttstock to hold the parts. Use cotten or cleaning patch
to keep them from rattling around. You need to use a little care to make sure you don't drill thru the stock but is is easier and takes much less work than creating
a pocket and then having to inlet a cap to hold the parts in.
3, inlet pocket in the forend of the rifle and then use a little piece of brass to make a cover to go over it and screw it in place.
Personally I prefer option #1 best but have used 2 on occassion with #3 being a last resort unless the rifle has a synthetic stock with lightening pockets already molded into the forend.
Good luck..
DonT