If you are just looking for the list of files, and the package you are working with is not one of the new-style "flat pacakages", then you just right-click on the pkg/mpkg and "show package contents", then inside the "Contents" folder look for the .bom file. Use the command-line lsbom tool to list the contents. If this is a mpkg then you might have to go into the Packages directory and then into the individual packages to find their boms.
If it is a flat-package, then you need to use xar to unpack the file first, then you can dig in for the bom.
Note that this will not cover any files that are generated in scripts, nor does it make it easy to actually get the files (they are wrapped in a CPIO file, and can be annoying to get ahold of without unspooling everything).
Or if you want to skip most of this you can just get Pacifist, and it will do most of the work for you.
Comments
If it is a flat-package, then you need to use xar to unpack the file first, then you can dig in for the bom.
Note that this will not cover any files that are generated in scripts, nor does it make it easy to actually get the files (they are wrapped in a CPIO file, and can be annoying to get ahold of without unspooling everything).
Or if you want to skip most of this you can just get Pacifist, and it will do most of the work for you.