I think the 4 things people generally look for in suicide is painless, quick, accessible, and reliable. However getting all 4 is pretty much impossible, except maybe if you live in a US state where getting a shotgun is very very easy.
If you want quick and painless, consider guns, nembutal, nitrogen gas.
More accessible would be hanging. Not quick or painless, but as far as the accessible methods go it's one of the more reliable and all you need is a rope (which you can buy at pretty much any hardware store).
People also talk a lot about sodium nitrite. I think it used to be easier to get before it gained popularity as a suicide method, but it's getting harder and harder to find now. You basically mix it with water and then drink it. Some people also take sedatives to help relax or antiemetic medications to reduce the chances of you just throwing it up. This has never really been my thing, but I think it's relatively tolerable as far as pain goes - most people seem to report a stomach ache. Takes some time though, as you have to wait for your body to digest/absorb it.
