Sometimes menus have to be built and rebuilt on the fly, such as for spelling suggestions.  When using actions to implement this, I like to define a special action group for the menu's actions.  Then the next time I have to rebuild the menu, I can just indiscriminately blow away the all old actions in the action group before building new ones.

The blowing away part is a bit cumbersome.  Currently you have to remove actions one at a time:

   list = gtk_action_group_list_actions (action_group);
   while (iter = list; iter != NULL; iter = iter->next)
      gtk_action_group_remove_action (action_group, iter->data);
   g_list_free (list);

A "remove_all" function for action groups would be a nice convenience:

   gtk_action_group_remove_all_actions (action_group);