A method that is highly and quickly accessible, peaceful, cheap, etc. As you describe is what most people are struggling with on this site. Most methods are limited in at least one of these, but it does vary which is why researching specific methods is worthwhile.
Hastily plannning/rushing your ctb is likely to increase the risk of pain, failure, etc. but I empathize with the desire to do so quickly.
If your chosen method is drug poisoning you probably won't find a reliable, peaceful, and readily accessible option all at once.
Most drug poisonings are less than 1.5% effective making it very unreliable. The few that are reliable (e.g., cyanide, detergents) are incredibly painful.
Likewise the ones that are peaceful and reliable (SN, N) are less accessible. You absolutely *can* find SN but you won't be getting it quickly as it usually mails from overseas and may require some significant time-consuming research online for where to find a source.
Opioids are more reliable than most drug poisonings but are still fairly unreliable due to individual differences in tolerance, street/dark net market impurities, etc.
I unfortunately cannot tell you other medications that tick all the boxes of accessibility, reliability, and peacefulness as there doesn't really appear to be any.
SN is most people's choice if they have access to it as the value of a peaceful and reliable death usually outweighs the time it takes to access it. But it's a subjective preference.
Hope this helps.