One way of going about this is to make a group out of these packages with a special policy, just as we have them for command line apps. Description mentions are IMHO not the best solution as it's too easy to skip/miss them and then you're left wondering why this stuff doesn't work. My first thought about doing it in the least invasive, but firm and informative manner is to use a bootstrapper/launcher - the actual app would not be started directly, but instead would depend on a (provisional name) external-game-data package (not in a user section) and would be required to start that from the .desktop file. It would also drop two files in /etc/externalgamedata.d/, a packagename.files and a packagename.info, the first containing the paths required, and the second that displays info where these can be obtained from. Then, when the end user launches the app, the launcher checks if the files are present, if yes, cool, launch game, if not, show info dialog which clearly states what goes where. Personally, I would maybe also require game data to be in MyDocs (so users could just drop it via USB), though this might encounter tech problems (due to VFAT limits). Thoughts ? I will gladly make such a launcher in bash if we have a consensus of doing things this way.