Absolutely water. Sealed 1-gallon bottles of distilled water are cheap, keep forever, and you can either drink it or use it in the radiator.
Keep the blanket.
A roll of duct tape. Don’t leave home without it. I also carry a roll of electrical tape just in case I need to fix a hole in a radiator hose.
A can of “leak-stop” tire inflator.
Fire extinguisher.
A couple of sealed granola bars. Replace them often.
Rope. I carry a 20’ heavy-duty tow rope and a 50’ lightweight rope.
Flashlight - with good batteries. Maybe even an extra set.
Several emergency flares and reflectors.
At camping supply stores, you can get a raincoat that stuffs into a small pouch. It’s more than just an emergency kit item. It can come in handy any time you get caught in the rain–as long as it’s in the passenger compartment.
A ziplock bag with some rubber bands, plastic zip ties, a cable clamp or two, a bit of string, a bit of wire, some paper clips, a disposable lighter, and various other little stuff.
A few miscellaneous tools, including a knife, a screwdriver (the kind with interchangeable tips, so you can have phillips, flat-blade, Robinson square drive and such with one driver), a small pair of pliers, and so forth.