Tylenol overdose. You won’t die quickly, it is slow and painful. You also may survive and be left with permanent liver damage that will possibly require you to be put on the transplant list.
Overdose on nbome's.
You'll decide that you don't want to die about halfway through the trip and then you'll be terrified and hallucinating while going out of your mind for hours until you die of heart failure.
Self immolation. Shit's terrifying and probably extremely painful. Also, there's a possibility that someone will save you and you survive with horrific burns all over your body.
Shotgun to the face is also pretty damn messy, especially if you survive. There's this guy that survived one such attempt who had to get a face transplant.
Any kind of drug overdose. Unless you know your drugs and are precise, it's all too easy to undershoot and make it an extremely painful, but survivable process, or to pick the wrong drugs and consign yourself to a long, drawn out and painful death.
tying a steel cable to a pole, weaving it through the back of your car under the head rest and tying the other end around your neck then flooring it and shredding your head off