What Is The Best Bill I Can Use To Euthenise

What is the best bill I can use to euthenise a cat. My cat has kidney failure, doesn't eat anymore, and was diganosed over two years ago with the disease. My vet told me that it was quickly approaching the "time."
I can't afford for a vet to euthanize him and I don't want to leave him at an "animal shelter." Thanks.

Brad