EMS will always ignore DNR .
It is a complicated medical and legal document . They're neither trained nor interested (nor bound) . They may take it to ER (not sure). As BPDBarb noted it's for terminal situations , usually for stable patients experiencing some 'organ failure' and need life support -- not for Emergency Room . Regarding advanced directive , it will be verified by more doctors and tests , so it's really not something you do with someone that just came in fighting for their life .
Malpractice and negligence are far worse than going against directive . Directive is to be practiced by the doctor that is responsible for a patient that is hospitalized in a ward . That's because they know the specifics , history , prognosis , etc . Can you imaging a hectic ER doing intubation iv cpr etc -- and then docs start to read a legal document? Not practical.
The use of multiple CNS sedatives had been discussed here and it's more likely to survive . Even according to your plan , questions of practicality -- take 500 pills , drink alcohol and opioids w/o vomit . Members here tried to OD and fine tune opioids-alcohol-benzo and couldn't . Sadly search option in site not working for me, in order to provide more information that was previously described :)
* If it helps , opioid ODs are either plug or IV