If you have access to something that can make you pass out easily, stand in a lake or pool or tub. If the drugs don't kill you, you'll drown while you sleep. I've tried it once, the adrenaline kept me awake and I didn't pass out, and if I did, I couldn't shake the fear that I would wake back up while I'm drowning anyway.
Back in high school, I beer bonged an entire 26 of jim bean. 750ml of whiskey instantly. I woke up the next day covered in black puke. I for sure had alcohol poisoning, but I wasn't lucky enough to choke on my puke in my sleep, and somehow my 16 year old body made it through it. That's how my favourite comedian Chris Farley died, choking on his puke in his sleep. A few famous people have died like that.
I think if you can make yourself pass out with something, it should be in area that kills you after you pass out. Like on the edge of a building or like I said in a body of water. I wouldn't feel comfortable with just booze and sleeping pills to kill me.