I agree with what the others have said already, I think it's incredibily difficult to make your suicide look like an accident. The best methods I can think of that would achieve this are drowning, death by cop and jumping into traffic. HOWEVER, I don't advise jumping into traffic or death by cop, as it involves bringing other people, or "innocent bystanders" (for lack of better words) into your death which is something I don't particularly agree with. That leaves drowning as the best option, but even then, your own SI will most likely betray you, and it may be difficult to pull off if you're unprepared.