Falling down from somewhere like 'hey i'm drunk af oooops' seems to be the best option, deaths caused by other people are not the best thing...
Taking wrong medication is an option too, but that doesn't sound like a fast and painless death, and one can ask himself why you didn't call the ambulance.
My idea was leaving a note that I'm leaving the country without a phone, never come back, never call someone, I'm just gonna leave everything behind since I can't bear it anymore, so please don't hope for me to call some day, it would screw my try to free myself from my old life. Be sure that I'll be fine, there are always helpful people around the world and I can care for myself. Goodbye
Something like that
'I have cancer and I want to travel and then die on my own will' would also be an option.