Are you a cheapskate or easily motivated by money? Set yourself a modest junk food budget for a month and track your spending. Set a financial reward for yourself (buy something you want) when you hit that target. Then set a lower target and a longer term reward. Forgive yourself if you go over, and don’t give up.

Junk food is so expensive now that you’ll blow through that budget in no time. Realizing how much this addiction costs you (like weed, smoking, drinking, gambling, etc) is often a great way to make the decision to kick the habit. Even if you can’t stay within the budget, keep tracking your spending. The goal is to reduce if stopping cold turkey isn’t your thing.

If this isn’t for you, what everyone else said might work too.