Something that's helped me was Indygirl's great quote (paraphrasing here): "If you received a traffic ticket, would you go around breaking all traffic laws for the rest of the day?"
That quote kind of brings it all home in a humorous way for me.
Don't wait for tomorrow; do it NOW! The very next meal is your do-over! Just say to yourself, "Well, that tasted good. Moving on! Now, what healthy thing can I plan for dinner?"
This way, you've acknowledged you ate but are not flogging yourself over it; gave yourself permission to move on so you're not stuck in the past; and most importantly, actively engaged a plan for the future - even if that "future" is a mere two hours from now. It kind of is pressing the re-set button.
So many of us are or have been trapped in that, "I'll-begin-again-tomorrow" rut. I know I was.
Then, like you say, tomorrow comes & if you flub at all, you repeat the same silly mantra of "tomorrow." Well, forget tomorrow!! Do it NOW and I promise, you'll feel more in control and feel better. And the better you feel about yourself, the more apt you'll be to continue making better choices.