200 Amitriptyline tablets, aka 6 grams of it, mixed with 300mg of diazepam would kill you, you got to crush both of these tablets and put the powder into water then drink it, this takes 36 hours though.
edit: You can mix 50-60 chloroquine tablets, 100mg of midazolam tablets, 300mg of zopiclone and zolpidem together and drink it. You crush all of these tablets and put the powder in water, 45 minutes before drinking take 3x10mg of metoclopramide
You can also take 6 or more grams of phenobarbital which will kill in 3 days