Seppuku
Get a big knife (a large kitchen knife would likely do, but make sure it's sharp) and cut your belly open with a cross. Then, thrust the knife upward, where if you're lucky you can pierce your heart. Either way, since your entrails are largely unreplaceable, the main reason of seppuku is to ensure that a doctor can't save you in case your suicide is reported.
Or you can just go to sleep on some train tracks. That works too.