RPM and DEB packages are both containers for other files. An RPM is some sort of cpio archive. On the other hand, a DEB file is a pure ar archive. So, it should be possible to unpack their contents using standard archiving tools, regardless of your distribution’s package format. Under normal conditions, you should use your distribution’s standard package manager, rpm or dpkg and their frontends, to manage those files. But, if you need to be more generic, here is how to do it.

RPM

For RPMs you need two command line utilities, rpm2cpio and cpio. Extracting the contents of the RPM package is an one-step process:
rpm2cpio mypackage.rpm | cpio -vid
If you just need to list the contents of the package without extracting them, use the following:
rpm2cpio mypackage.rpm | cpio -vt
The -v option is used in order to get verbose output to the stdout. If you don’t need it, you can safely omit this switch. For more information about the cpio options, please refer to the cpio(1) manual page.

DEB

DEB files are ar archives, which contain three files:

• debian-binary
• control.tar.gz
• data.tar.gz

As you might have already guessed, the needed archived files exist in data.tar.gz. It is also obvious that unpacking this file is a two-step process.

First, extract the aforementioned three files from the DEB file (ar archive):
tar vx mypackage.deb
Then extract the contents of data.tar.gz using tar:
tar -xzvf data.tar.gz
Or, if you just need to get a listing of the files:
tar -tzvf data.tar.gz
Again the -v option in both ar and tar is used in order to get verbose output. It is safe not to use it. For more information, read the man pages: tar(1) and ar(1).

If anyone knows an one-step process to extract the contents of the data.tar.gz, I’d be very interested in it!

Update

tar p mypackage.deb data.tar.gz | tar zx