Adjusting planned meals throughout the day

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In an effort to keep unhealthy choices at bay I strive to plan my day's eating in advance, usually the night before. My problem is after I make a plan I have such trouble sticking to it! I might get up to grab the apple and peanut butter snack I had planned for, but end up grabbing something totally different and need to keep updating, updating, updating.. it's exhausting! The problem is, if I don't pre-log I can see myself easily frontloading my calories and having only a miniscule amount left at dinnertime.

Anyone else face this problem? Any tips or tricks for how to stay on track?