In addition to the MultiLineToolbar I’ve needed a way to group actions into submenus for better usage of the space of the toolbar. This plugin can easily add new submenus aka categories to the toolbar. It adds a new menu to the context menu of the toolbar to add the action the context menu was opened on to a category.
The action can be added to an existing category or a new category can be created. The actions in the submenu will have the order they were added to the category and the category will sit in the toolbar at the location of the first action in the category. The category will also have the icon of the first action.
To move the actions back into the toolbar the category can be reset via context menu of the category. When resetting the category all actions will be put back into the toolbar and the category will be deleted.
There are no other settings to keep it simple.
Source code can be found here: https://github.com/ds10git/josm-toolbarcategories-plugin