I’m just wrapping up a year of maintaining my bullet journal practice using index cards instead of the more popular notebook form factor. It’s heavily inspired by the century+ old Memindex method.

AMA

Sample bullet journal using index cards featuring a daily card with schedule and to do list items sitting next to a card index and a Pilot Hi-Tec C Coleto multipen

Card index daily journal and planner with 4 x 6" index cards separated by divider tabs labeled from Aug through Jul of following year.

Green canvas Flatty Works canvas envelope-style case with a clear plastic front through which one can see a handful of 4 x 6" index card dividers and index cards.