Hey wisher!
Wow, what a day!
I'm with the others who say that better planning would help. Clearly you can't control your work environment--but you can make sure you have better foods available for those days when breaks are hard to come by. Snacks like Kashi bars, FruitFast bars, and other healthy food bars come in handy, and they keep indefinitely if the wrapper is unopened. Other ideas: slice up an apple and put it in a zipper bag. (If it goes a little brown, that's OK--or you can put some lemon juice on the slices to prevent that.) Peel an orange and put the segments in a zipper bag. Hard boiled eggs also come in handy, and they keep for a day or so in the shell without refrigeration.
Making sure you drink enough water is also a good idea.
The general rule is not to average below 1200 cals a day--but as others have said, a day now and then that is too low won't necessarily do any harm. Still, it's not a good idea just because you get too hungry, and then it's too easy to swing into overeating to compensate.
On a day when you've only eaten 650 cals, I'd think that exercise is probably not a good idea. When the body has too few calories to work with, it will burn muscle as well as fat, and that can be counterproductive.
Hope this helps!
Jay