Singletrack (Shaun Murray) made this posting on SourceForge:

In Menuman, edit the Product menu entry

/index.php?module=fatcat&fatcat[user]=viewCategory&fatcat_id=1&module_title=announce

Change fatcat_id to match the id of "softdrink"

Change module_title to be that of whatever module you're linking to eg. announce, pagemaster, linkman, photoalbum.

In an ideal world, you could miss off module_title and it would list all modules that match that category but it doesn't.

See the full posting here:
https://sourceforge.net/forum/message.php?msg_id=2143569

My comments

If you have direct access to your database, the fatcat_id can be found in the mod_fatcat_categories table, look for cat_id.

I use this feature to show my links in a certain category, directly from the menu.
See this in action.

Singletrack has posted a RFE at SourceForge and even advised how to get the fatcat_id to show in in admin page.

Check out the post and the solution at SourceForge.