For liquids or items in single container (milk, yogurt, mayo), treat the container as both bins. Split it visually with halfway mark.
The concept:
- Top Half = Active Bin (you’re safe)
- Bottom Half = Reserve Bin (buffer period starts)
The trigger: Moment liquid crosses halfway mark (or your Restock Line Formula), add to list.
Why it works: You’re not “out” of milk yet. You’re “out of Active Bin.” Bottom half gives buffer time to shop before actually running dry.
Visual Marking
Use rubber band, tape line, or sharpie mark at halfway point. Or calculate using Restock Line Formula for precision.
Example: Gallon milk. You use 1 cup/day. Shopping frequency is every 5 days.
- Restock Line = (1 cup × 5 days) + 2 cup buffer = 7 cups = just under half gallon
- Mark at half-gallon line
North: Where this comes from
- Two-Bin System (parent concept)
- Fuel Gauge (empty vs reserve tank)
West: What’s similar?
- Gas Tank Reserve (switch to reserve triggers refill)
- Battery Indicator (color change at threshold)