The users group is the only group really required, these days most desktop environments / window managers use polkit(policy kit) to control who can perform actions such as shutdown and mounting flash drives etc without root. Generally polkit is configured by default to allow local users (those not remoted in through ssh etc) to perform these actions.
Some desktop environments such as enlightenment didn't launch a polkit authentication agent by default in openSUSE 13.1 or the authentication agent that is launched isn't currently installed. My openSUSE 13.2 machine has the packages, polkit-gnome, mate-polkit and polkit-kde-agent-1 each are polkit agents that you can run at startup to register your session.
I would expect that on kde and gnome this should work out of the box, if not you should create a bugreport on the openSUSE bugzilla, if you are using a different DM/WM try running one of the above agents and see if that resolves your issues, there is a chance that your DE/WM does not yet support polkit in which case you are going to struggle to do most of these things it is hard to provide more specific answers to your questions without knowing the DE, if you tell me i will try to update this answer accordingly