what items would you include in in the smallest lightest kit, similar to what goes in the original .mil stock cleaning kit, but improved.

I got oil in the grip. The type doesn't matter. Using a small contact lens solution bottle.
and:
Boresnake
Chamber brush
bronze brush for the bolt
pipe cleaner
1 q-tip

can't think of anything else.

It’s not exactly the same but I keep a USGI compass pouch in my LCE full of maintenance stuff for all my weapons.
-.308 bore snake
-5.56 bore snake
-.45 bore snake
- 2 small rags
- smith’s pocket pal sharpener

This is in addition to the kit kept in the rifle, which is:
M1A
-Combo tool
-Cleaning rod+handle
-Tube of grease
-Cleaning patches
-Chamber brush

AR
-Tiny bottle of lube
-A single section of cleaning rod+handle
-Bore brush
-Chamber brush
-Cleaning patches
-Double ended brush
-3 pipe cleaners
-Small baggie of pins, detents, and springs in the grip

Piece of weed eater line about 12 inches longer than barrel  with one end melted into a ball and the other end sharpened to a point.
A few patches
Toothbrush
Small bottle of CLP

A USGI compass pouch is an interesting idea. I need to add a rag to this formula here. And some cleaning solution. I don't like to use multipurpose things.

Little patch of T shirt, boresnake and CLP is all you need

What’s wrong with a round Otis M16 kit and have everything you need.

I'd add a rod or cable that can remove stuck cases and or squibs.

I acquired a few Otis kits at one point. I like the multical one. Does me for 22lr to 12ga.

Two issues, which can be remedied. First, you need more rod sections for bore obstruction or stuck cases. Second, you need an AP brush head.

Otherwise, it’ll get you through.

There’s enough room to stuff in some patches and qtips.

Everyone hates carrying rod sections. Soft lines can’t clear a barrel. I like having both in the otis kit. Things only like the size of 2 dip cans. But really, most of the otis kit is dead space. I don’t need 22, 30, 9, 45, and 12 brushes. You generally just need two sizes. You generally don’t even need a brush just to be out in the field, but of course you would if forward deployed. You don’t really need to have the pistol length line either. Two rod sections or suck it up with the rifle length line.

I’d argue that you really don’t even need the qtips most of the time. If you’re truly out in the field, you’d want to save them for removing dirt from your locking lugs, and you’d really only use two patches to clean, one to wipe out any dirt in the bore and one to get some clp down there.

You should be going out in the field with a clean, lubricated weapon. Dust on the outside just looks bad. Fouling on the inside isn’t an issue if you throw a few drops of CLP on it. You should be able to shoot more ammo than you can carry before needing to actually strip the gun and clean it. Should you actually burn through a combat load, put 3 drops into the crevice between the bolt and carrier, and 3 drops on the locking lugs. Back in business, don’t even have to unload the rifle if shit’s that serious.

Even better if you can drip some oil on the cam pin, and rails.

Anyway, OP, if you really want the lightest, tiniest kit, with the best true utility… I’d get the otis rod sections, the correct brush and jag/eye for your rifle and pistol, otis brush (toothbrush head threaded for their rods), patches and qtips. You’d use your tshirt as a rag if you really need to cut size/weight. Don’t use your socks, you want them to always be as clean and dry as possible. Socks are the most important article of clothing.

Make sure you have at least one extra rod section, and they’re all male/female. Otis has some female/female sections that are basically useless, I have no clue what they’re for. You want the extra section because inevitably, one of the ends will get screwed up and be useless.

The nice thing about otis rod sections, is that they are pretty small. Having 6 pieces instead of 3 like a GI kit is annoying, but GI rods are in theory much harder to pack, because of their length. I believe the otis rods are also brass, unlike the steel GI, so they shouldn’t scratch a muzzle crown easily. However, as noted, being brass, one of them is liable to get dicked up so you need an extra piece.

What is the weed eater line for?

A pull-through I suppose

Piece a patch and pull through?  I’m confused.

Boresnake and oil is all I carry for camping/ hunting trips.

The sharpened end is used to pierce the patch and you then slide the patch down the line til the melted ball on the other end stops it.
You can then use the line to pull the patch though the bore kinda like you would a bore snake.
This method is often used in cleaning air rifles which have barrels make of fairly soft steel but it will also work as a field expedient method for cleaning powder burners.