There's a lot of considerations, obviously it varies person-to-person but the following are some things that may be helpful for those who are planning/getting their affairs in order.
Disposition of remains: If you wish your remains to be taken care of in a significant way (cremated, burial funeral, etc) then make sure you write that in a will or last statement. If you wish for certain individuals to have some of your things (certain clothes, tools, games, etc) then again make sure it is in a will or statement because without that then it's up to the next-of-kin who may not know your wishes or may decide to take another course of action.
Do I need a will? Make sure if you have assets in excess of $30,000 (if you are in the US) you put them in a will, if you have life insurance, IRA accounts, etc that you designate a beneficiary. It depends by state (in the US) but if you have assets greater that $30,000 but not a will then your assets go to probate where any outstanding debt takes priority, everything is subject to court costs and lawyer fees, and your family has to go through some frustrating and complicated hurdles to get anything of value and/or settle your debts.
There are generic will's you can buy at some office supply stores, there are some online services that cost a small fee ($35 or so) if you want to make sure you do it right.
Pets: If you have a pet it is considered property in the eyes of the law so you need to designate a caretaker for your pet(s) and can also allocate some funds from your estate for its care. Please note that if you CTB and there is no one there to take care of your pets they may be taken and put into a shelter.
Life insurance: If you have a policy ensure that it is two years old before CTB as most states (with the exception of one or two) require the policy to be two years or older to pay out in an instance of suicide. I would also look at your particular policy to see if there are any other exceptions.
Financial accounts (credit card, banking, loans, retirement, medical savings etc) I would write down the account numbers, it's expected asset value (or debt), and your log in information if there is any. Your family or loved ones may not have access until they get a death certificate which can take quite a bit of time in some cases.
Property: If you have a car, boat, house, real estate in your name make sure your family or whomever will have access to your deed, title, etc of that property so they can take possession of or begin the process of taking care of your assets. If you have a car or home that you are still paying on: it can take months to get everything taken care of and your lenders will still expect payment so to prevent repossession or foreclosure/late fees/additional costs that will come out of whatever assets you leave behind then I really advise you have this information available to whomever will be handling your estate.
Why does it matter? Putting your affairs together can be a pretty tedious and lengthy process, If you are leaving behind family or friends that will be taking care of your assets when you CTB I strongly encourage you to take the time to get everything together. Your friends and family (no matter how estranged or little you think of your current relationship) will very likely be having an incredibly hard time with your passing and all of this will help them through the process since grief can make it almost impossible to do anything productive.
Sorry for the long-winded post. Just some general advice that will help make sure your last wishes are followed and to help out any friends or family through the aftermath.
