And the remembering is done by means of a list on your phone. When you run out, add it to the list. When you're at the store, check the list.

Not techy enough for ya? Think of it as preserving state and passing it across time from "the you who knows" (senses a need) to "the you who does" (is at the store). Or as asynchronous communication with yourself.

The way this works is: when you run out of your primary X and pull your backup X out of the closet, you immediately add X to the shopping list you carry with you. Then when you're in a shop, you simply buy things that are on the list and put them in the backup closet.

This requires developing two habits: 1) adding a thing to the shopping list when you fetch the backup item, and 2) actually using a shopping list.

Now I sympathize with the fact that different people have problems with different habits, so if it really doesn't work for you, then I guess you need something else :). But the benefit of this trick (or "life hack") is that it's free to use, doesn't require any purchase to set up, and doesn't tie you to any vendor.

Automation means you actually have to run out to get more.

A backup bottle means you never are out - if you remember any time during the 2-month period it takes to use up a bottle. Or have an automated system.

I've actually semi-automated this in the past by having Amazon ship me products on a regular schedule. Pricewise, though, it makes more sense to just make a quarterly trip to Costco and load up the storage closet.

Because you are not beholden to billions of dollars of infrastructure just "working".