Loading the bike batteries into the Rolltop Cupcake Box reminded me I hadn’t updated the Lip Balm Holder around the latest tube of sunscreen. My excuse was I didn’t quite know how to model the not-quite-elliptical shape of the Coppertone sunscreeen tube in OpenSCAD, but now I can bypass that whole problem:
The trick is to scan the bottom of the cap to get a high-contrast image:
Import the image into LightBurn, draw a circle tangent to the outside of the cap’s smaller diameter, turn the circle into a path, drag the nodes and twiddle the control points to create a symmetric shape just outside the cap, then outset the result by 1.5 mm for clearance around the tube:
That 3 mm of wiggle room lets us drop the tube into its socket without careful alignment.
The lip balm tubes all fit into 18 mm circles requiring no special design skillz:
The mid-left oval goes around the Coppertone tube.
The top-mid drawing shows the 3 mm outset around each of the pieces, with the smaller tubes arranged to put their midlines tangent to each other and the oval tube. LightBurn does not, as far as I can tell, have a direct way to align a shape tangent to two other shapes at the same time, but iterating at increasingly absurd zoom levels gets the job done fairly quickly.
Welding those shapes together produces the top-right drawing, which serves as the template for the lower set of layers.
Deleting the inner details produces the mid-right blob for the bottom layer.
Most of the layers come from 3 mm plywood, with edge-lit acrylic on the top and bottom surfaces:
Mary pronounced it better looking than the 3D printed version, which I agree clears a rather low bar, but it suffices for the job.
The LightBurn layout as a GitHub Gist:
The Smell of Molten Projects in the Morning 
For sure… next year Coppertone will change the size or shape of the container maybe both.
Ah, but now I have an algorithm! [grin]
On the plus side, you now have a rough model for an oddly shaped set of brass knuckles.
Bonus: motivation to get a CNC plasma cutter!
Lip Balm holder?
That shape looked somehow familiar.
https://en.wikipedia.org/wiki/Brass_knuckles
I swear that was entirely coincidental: I only noticed it after cutting the things out!