Every person, no matter how young or what their financial situation, should have a will. Even if you are in perfect health, there is always the possibility that you might be involved in a car accident or similar low probability event that might result in incapacity or death.
The first issue that is important is expressing your wishes concerning what should be done with your body. Perhaps the most important decision you need to make is what should be done if you are brain dead, in an irreversible coma, but your body can continue living by being hooked up to expensive machines. Would you wish doctors to try everything possible to keep your body alive even in the case of irreversible brain damage or not? A living will or advanced directive allows you to make these decisions rather than have them made for you.
Another issue is funeral arrangements. Would you want to have a religious funeral or not? Do you prefer burial or cremation?
Next, if you died or experienced brain death, would you wish to donate your organs, to help other people live? Every donated organ can improve the length or quality of someone else's life. In your will, you can specify your wish to be an organ donor.
Finally, a will allows you to make specific bequests, sometimes of small things that can make people very happy. For example, you might wish a close friend to have your music collection or a piece of sporting equipment that has a special meaning.
Normally, if you die without a will or "intestate", and you are single with no children, your parents will receive your entire estate. Taxes on your estate will often be higher if you die without a will.