It is technically possible. There are a lot of relatively benign things you can eat/drink yourself to death. You can die from drinking too much water in a short time... look it up. But, your body isn't going to like eating all that salt. You probably end up sick and vomiting before you eat enough to kill you... but you might make yourself hurt quite a bit anyway. I was honestly looking into this for a while, because it is obviously a cheap method and one that you could legally obtain anywhere... but it just seemed in the end like it was going to be really difficult and high-risk low-reward.