But that's weaksauce and boring. You don't want your suicide to be lame, now do you?
Like, if you can still operate a car, get a convertible with cruise control, grab a long piece of sturdy wire, a molotov cocktail and a bottle of superglue.
You then park somewhere near the highway, put the loop around your neck and attach to a signpost, speed down the highway and then you must act quick:
Use the Molotov cocktail to set the backseat on fire, hit the cruise control and superglue your hands to the steering wheel before the wire tears your head off.
The burning convertible will race down the highway, driven by a headless, burning corpse... if you kill yourself, at least make it interesting for the news reporters goddamnit.