Send information that matters to the business - patching details, server uptime (not workstations), tickets logged and closed ticket info, time frame for ticket closure (careful with this one depending on your billing structure - some clients get weird seeing quickly closed tickets "Why am i paying hourly/monthly for 20 mins support? etc..), Outline of preventative tasks - temp cleanups, Backup status and results.
Perhaps mini roadmap for application updates within your control - (office etc)
Flag systems with no warranty or expiring warranty and installation/setup dates and suggested replacement timelines - perhaps quarterly?