The low-down and high points:

POA, living will, will, care measures (this is a new[er] list that adds if the person becomes incapacitated if they wish for palliative (comfort) care, IV fluids, a feeding tube of some sort, etc), DNR/DNI (do not rescucitate/intubate, which ARE two very different things), funeral plans, and anything else important.

It is very important to know WHERE TO FIND THESE DOCUMENTS. We have had personal family problems in the past with someone making an unofficial will and putting in a certain place, only to have his daughter throw it away in the trash [on purpose], rendering it a useless piece of paper and defaulting every posession to her.
-Her attourney advised her to do this, by the way.

So, get a notary for an afternoon (if he can handle it) and go over everything. We had to do this with my grandmother, but you might be surprised by what they have to say.
I, being only 23, have already written out mine and made my wishes clear and known to my parents what I want in the case of the papers being misplaced or mishandled.

Place your name on the bank accounts as joint accounts. This is a simple procedure that can be done in 10 minutes with the persons permission. If they are not mentally stable enough to give you consent, you can obtain a doctors letter to state this problem to your bank. You still have access to the accounts if they die suddenly, though some holds may still be placed on the account(s). However, you may also wish to place some of the money in a separate account to have in the case of sudden passing and needing it for funeral and other expenses.

Also, hospice can be used in the cases of people without terminal illnesses at the time. I work on neuro, and see people come in with massive brain hemorrhages and other problems, which render them completely debilitated at much younger ages, go home or to a facility on hospice. Do not rule this out just yet; something tragic may happen.

It is much better to know a loved ones wishes than to wing it.