@LostGirl ,
CO can be good if you can be sure CO levels are high enough and the process of dying will not be interrupted.
Small car is good, large car: unsure. Sulphuric acid and formic acid can also work, check posts. I'm not sure about the 'mechanics'/process of the latter.
SN: decent choice, 15 gr most likely. Cimetidine or ranitidine for stomach acid, take the proper antiemetic (meto?), timing, and since it can also be very distressing something that sedates but doesn't mess you up may be helpful. High dose of benzos ? Just don't let it interfere with the SN.