You can solve this problem without installing any additional software. Here's how...
I wasn't sure at first if my problem with .pkg files the ones described in this thread, but then after reading the whole thread I realized supto_o has exactly the same problem I have.
To clarify:
I have a .pkg file. When I right click there's no "Show Package Contents" in the pop-up menu.
Yet I can run and install the .pkg. I have no idea what files were installed or where they were installed. I need to see the contents of the .pkg file. My blood boils because it's incomprehensible to me why Apple would keep contents of a .pkg file from being inspected.
My solution:
On a lark I tested the file to see if it was just a tar file, and sure enough it is! So try this:
$ tar tzvf yourfile.pkg
If you do you'll see someoutput like:
$ tar tzvf base-crypto-1.10.0-x86_64.pkg
-rw-r--r-- 1 jan staff 44679 Nov 1 19:06 Bom
-rw-r--r-- 1 jan staff 2505614 Nov 1 19:06 Payload
-rw-r--r-- 1 jan staff 87 Nov 1 19:06 Scripts
-rwxrwxrwx 1 0 0 565 Nov 16 16:24 PackageInfo
great! So then extract that, because what you just was was a listing. So run the same command, replacing the "t" with an "x":
$ tar xzvf ../base-crypto-1.10.0-x86_64.pkg
x Bom
x Payload
x Scripts
x PackageInfo
Now you can peek at the file PackageInfo to see where the files are installed:
$ cat PackageInfo
<?xml version="1.0" encoding="utf-8" standalone="no"?>
<pkg-info overwrite-permissions="true" relocatable="false" identifier="org.freedesktop.gstreamer.x86_64.base-crypto" postinstall-action="none" version="1.10.0" format-version="2" generator-version="InstallCmds-554 (15G1108)" install-location="/Library/Frameworks/GStreamer.framework/Versions/1.0" auth="root">
<payload numberOfFiles="63" installKBytes="5953"/>
<bundle-version/>
<upgrade-bundle/>
<update-bundle/>
<atomic-update-bundle/>
<strict-identifier/>
<relocate/>
Hope that helps.