So I tipped them out and started from scratch.
I used a the same technique that I'd used for my nail polish storage - I cut strips of thin card and cut notches halfway through each strip.
I slotted the strips together. (As you can see, I started out using coloured card but switched to white when I ran out.)
The grid fits into the box ...
... and keeps my lipsticks, lipglosses and essential oils organised.
And because we all love a before-and-after shot, here's one to end on: