Then write it down as x2-x2.5 of what you'd expect. Better to eat less the following day than overeat.

Statistics work in your favor here though: at 2,000 kcal a day over a month, you'll consume 56,000 kcal total. So the question isn't whether any given thing was or wasn't some value - it's how much of a buffer is in your "unknown" chunk of that month that you're not winding up way out.

Like if you just tracked the things you can track, and noted the number of occurrences you didn't, then your end of the month weight will tell you whether you're overshooting or not, and you can estimate what proportion the "unknowns" might represent (and whether you should put a conscious effort into reducing them.

The estimating is often enough to make better choices.

I know I’m not going to be able to eat my main, a couple slices of pizza, one or two entrees and a dessert with only 800 calories left in my budget.

Sure, I might be somewhat off in my estimate, but in practice, I might forgo the entrees and dessert (or share a bite from someone else), set some of my main aside to take home, and have a slice of pizza.