Ctrl + I (Only for vessel users) will open a dialog where you can reset system files. This will reset the system itself. All functionality, menus etc. If you are receiving error messages onboard the vessel, ctrl + i and Reset system files is your best bet. If you are ashore, ctrl +F5 will do the trick.
Ctrl + U - Will force update all data in the system such as Reports, checklists, governing documents etc. If you are missing a report, or it seems to have an old title, ctrl + u is your go-to-move
Ctrl + H - If in edit mode of a report/audit/f&c or similar, this command will open up History tab to show a timeline of changes of the current entity.