Linking Calendar to Event info and Expenses

We store team/client activities in a calendar. So… event on March 1st shows the client, the project lead and the activity. I’d like to be able to upload receipts and a overview of the activity and link it to the calendar… so when we browse the calendar (eventually by client or project lead), we can see or upload the overview doc and any receipts.

I have managed to link to the calendar successfully, but not found a way to “ref” the calendar entry in a new expenses table or a docs table.

Has anyone tried to do this sort of linking to a calendar data source?