Relying on willpower?

When I have an urge to eat, I sometimes respond to the urge with a thought such as “I don’t care” or “I can just have one” or “I’ll go back on plan tomorrow.” And the urge is so strong that it feels easier to give in to the thought and just eat off plan rather than respond with a more productive thought. It seems that following through with a more productive thought requires willpower. Since willpower is limited, how can I approach the situation in a way that doesn’t rely on willpower?