I keep something similar in both my vehicles, but a few years ago I changed from carrying a lot of general purpose
stuff to a little bit of it (e.g. vice grips and a crescent wrench) and then the exact tools needed for specific tasks.
As an example, my battery can only be removed with a socket on an extension based on the location of the hold-down,
so I carry a ratchet, extension, and that specific socket for the battery, along with a combination wrench of the size
needed for the battery terminals. I've done the same for fan belt changes (along with the spare belt), and for
tire repair (plug kit) and changes.
I went through every road failure I had in my life, as well as looking at what AAA and other roadside places say
the common failures are and then made sure I had the exact tools to take care of those events. I've found the
bigger issue after the obvious problems (battery, belt, hoses) is that it's unlikely you'll have parts on hand for the
repair unless it's something very common and specific to your car, so once repair involves going to get parts, you're
in the position of getting the correct tools as well.
So my advice, rather than tell you to add a ratchet and a gator grip socket or whatever, would be to see what
you need to do at least a battery replacement, a belt change, and replacements on any hoses, and then ask
yourself if the tools you have will do the job. As an example, I ran into a snag once where I needed to remove
a constant-tension spring clamp from a hose, which pliers or vice grips can do in a pinch -- but the clamp was located
in a place that neither of those tools would work, so I had to use a special spring clamp tool. In this case, instead
of packing that tool I changed out the clamp and repositioned it so that I'd have easy access to it in the future.
This is stuff you don't want to learn on the side of the road, which is why I suggest simulating (or doing if you're
performing actual maintenance) everything with the tools and parts you carry.
That said, I'd probably add some JB weld stick to the kit, and zip ties, and a short bit of safety wire (enough to tie an
exhaust pipe back to the hangar.) Some 550 cord probably wouldn't hurt either.