When I prepare a Pork Shoulder for serving a a future date I do the following.
1. I pull the meat while it's hot.
2. I then take softball size handfulls and wrap them in plastic wrap. Be very carefull to not pack it together. You want it loose so that the heat escapes quickly, you need to move it from 140 degrees to 40 degrees (the danger zone when germs grow) as quickly as possible.
3. I place the balls with space between them on a cookie sheet and then set that in the freezer. I don't let them freeze but keep checking them until they get to 40.
4. At forty degrees the balls are gathered and placed into either plastic tupperware, the disposable kind, or 2 gallon zip loct bags and placed in the fridge.
5. If I'm reheating all of it I would use a dutch oven with a tight lid, add 1/4 cup of water or liquid of choice to create a moist environment. Put the lid on it and into to the oven at 200 to 225.
6. Service when it is back over 160. Stir now and again.
7. I use the dutch oven as the mother load and transfer smaller batches to a crock pot to keep it hot and serve from.
Hope that helps, if the entire Butt is already chilled I'l sure someone will chime in.