I would toss in a multi tool of some kind - sometimes a screw needs to be tightened or (pliers) a clamp fixed? Also as most break downs seem to be at night an extra flash light couldn't hurt.

I will second Jeanette Isabelle and have a bottle of water along with some hard candy just because it helps pass the time waiting for the tow or help to arrive. Second also on the sleeping bag vs. the blanket but having both would be my go-to.

As we have a dog I've always got an extra leash in the glove box with a small dish for water so the pup can drink too and a few treats. Funny thing is I've used the extra leash several times when I found a stray that needed to be rounded up and taken home.

Paul -