They already weigh enough for how many are typically needed. Less flipping through inventory pages and containers is desirable.

Ditto for the lizard healing charms.

As far as I'm aware, this cannot be done.

That is sort of true. Items made with base type "Misc. Thin" can not be stackable. But if you are willing to make it a different base type it can be done.

Base type "Healer's Kit" might be a good one.

Actually I see the effects of Healer's Kits are hardcoded. You'd have to get more creative than that to get these to stack. Silly.

As an aside, you can make +50 healing kits.

Using the base type "Healer's Kit" would be ideal, except that the only effect that can be attached to those is the built-in Bioware healing kit effect, which doesn't seem to be easily overrideable via scripting.

Can't be done. Something about the way the stack interacts with an OnUse.

You wind up using the entire stack.