Another that I'd add to the list is umbrella insurance (a.k.a. excess liability insurance). This comes on top of your homeowner's and auto insurance policies and requires certain fairly high liability benefits from those underlying policies since the umbrella kicks in only above those levels.

However, say you have, e.g., a $1M net worth and buy a $1M umbrella policy. Then, your kid takes the car out and, heaven forbid, hits a cardio-thoracic surgeon who makes $1M/year and is driving a $150k car with his wife in the passenger seat. Said surgeon is laid out for 6 months, so you're hit with a loss of $500k just to cover the surgeon's loss of income. Another $250k each for the surgeon and his wife's pain and suffering, and $150k replacement cost for the surgeon's car.

Your auto insurance has a $300k liability benefit. The carrier, looking at the $1.15M claim decides to pay you the $300k and let you deal with the remaining $850k loss. This wipes you out financially.

However, if you have that $1M umbrella, the insurer will likely fight tooth and nail in court and out of court to get the case settled for, say $0.50 on the dollar. Essentially, they have an $850k incentive to do this. Even if they lose (which legal fight costs you nothing), the $300k from your auto policy and $850k from your umbrella cover the full claim.

And the best thing is that this policy will likely cost you just $30/month!