Ideally we'd all eat a perfect breakfast, but if you're not a morning person, that can be pretty tough. Because our bodies need really those nutrients, grabbing a pastry is much better than simply skipping the meal entirely.
In fact, if the coffee/doughnut cart is your only option, you can sort of (and that's a really big 'sort of') make it healthy. A donut gives you the fuel you need to make it to a healthy lunch. Go with a plain glazed treat, as that's 260 calories. If you combine it with some protein, like skim milk, your blood sugar spikes are regulated.
Eating that donut is certainly better than starving, which can lead to overeating, being forgetful ... and just plain being a cranky brat at work.