• A few spare buttons of various sizes, since you can lose a button and be unable to find it.
• Some straight pins to hold torn edges or a patch in place while you sew.
• A few safety pins because sometimes it's more expedient to pin now and sew later.
• A thimble because pushing a needle through tough fabric can be painful on your fingers.

Wax thread thingy. Dunno what they're really called, but it's a bit of wax in a plastic jobber with guides so you can pull the thread through.

Lets you thread a needle easier, and makes it go through various materials easier as well

Thread picker can be useful as well for, well, unpicking things or just poking things. Some small patches, possibly self adhesive ones are useful for larger holes. Possibly some safety pins for helping to hold things together while you work.

best I can do is an EDM sewing kit

I also have a spare button. The most... unnoticeable one that would fit most of the shirts I usually wear.

Disclaimer: old dude speaking, I don't wear t-shirts much or only under a shirt ;)

It’s not really sewing anymore, but if you wear a lot of knits it might be worth having a “needle for fixing pulled threads”... I don’t actually know what the proper name is in English, in French it’s called a “rentre-fil”. Examples 1 and 2.
It looks like a needle, but without a hole, instead having a “rugged” part that allows you to catch the thread and pull it through the fabric/knit so that it’s not visible anymore and doesn’t get damaged further.

I’m not sure if what I’m writing makes any sense, ha ha.