Are there any necklaces out there that are (or look like they could be) bags? I feel like I've looked everywhere.

Can you clarify if you are looking for bags that look like necklaces, or bags as regular accessories in the Glasses bin, or bags in the Jewelry bin categorized as necklaces?

There's an alternative here, which is a pose/prop box that adds the accessory and a pose to the arm. It works with most animations/poses ingame, and is a neat alternative to regular accessories. Not too many options for the bags, but they can be recolored. Both parts are needed.
https://modthesims.info/d/351006/co...-prop-hack.html
https://modthesims.info/download.php?t=351524

No, I mean an actual bag worn around the neck. Or a pendant that looks like it could be one. Preferably binned as glasses since I don't have BV, but if one exists as BV jewelry, I could try to learn how to un-BV it.

I was thinking entirely in the wrong direction...

So more like this, but as an accessory? (haven't found one yet, but came across this while looking)
https://modthesims.info/d/287583/drawstring-pouch.html

You could have a look around Medievalsims. If it's anywhere to be found, that's one of the places I'd think of first.
https://www.medievalsims.com/forums/viewforum.php?f=37

Yes, exactly.