I think you'd have to just intentionally infect yourself with a deadly disease or eat something that can kill you but that could accidentally end up in your food if you want to make it look like an accident.
The problem with that, or some other form of suicide that could be made to look like an accident (I was thinking of maybe getting into a car wreck) is that you're probably going to end up having to choose something that may not be certain to succeed, or worse may leave you crippled for life or in debt (like a car wreck or disease could).
Why do you want to make it look like an accident anyways?