There's one bucket list item most people don't check off. It's not taking that trip to Paris, but making their will.

Only about 40 percent of adults in America have a will, which is likely due to people not wanting to be reminded of their own mortality and that life will go on without them, says Jeff Gorton, a certified financial planner with the Gorton Financial Group in Oklahoma City.

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Why you need one: If you die without a will in New York, assets follow the "intestacy laws" of the state. Translation: A defined portion might go to your spouse and your children. "This may seem OK, but if you have children who don't have the capacity to manage money appropriately, it could be problematic," says Joseph De Sena, an Ameriprise adviser in Melville.

What does a will do? It states who gets what, and it's where you name a guardian for your minor children.

What can't a will do? Property with a designated beneficiary, such as life insurance, doesn't pass per the terms of your will, says Harold Bollaci, an elder law estate planning attorney in Garden City. You can't intentionally disinherit a spouse through a will.

Avoid mistakes: Give smart. Says De Sena, "Leaving money outright to children who have special needs may not always be the best option. Your will should contain a provision to establish a special needs trust to provide financial resources for them. Also, a financial windfall for an elderly person may delay or prevent them from receiving home care or nursing care from the state."