http://nguipxnkrp3qrzrlduhsatpcpwehnblzmlkc5ifiumxq4z5jlh4lwvid.onion/os_archive/os_OPSEC_357.html
I consider personal financial information ( like taxes, income, planning, purchases, etc) to be in this category that requires an airgap. Anything to do with planning, inventory or income sources ( what books you have in your personal library, how many "things you own", un-booked travel plans etc...), part time revenue etc, stock picking and purchasing plans, business plans, business ideas etc.