There were only a few lines to change in fact... One small change in calendar::item::get and some more changes in calendar::do_notifications. Passing in the package_id would be an option, but then i had to change calendar::item::new as well and i wanted to make as few changes as possible. As Don pointed out, after querying the database for the package_id, all other info can be retrieved via site_node utils. How could i contribute that change (might be quite useful for others)? Make a patch for a bug-tracker item?