One of the signs I'm getting older is that I need to keep a better eye on my diet. Fast food does unpleasant things to my digestion. And I really can't deal with sugary breakfasts anymore. If I have a doughnut or one of those individually-wrapped convenience store pastries, I'll be ok for an hour or so, and then I'll crash and be out of it for the rest of the day.
My ideal breakfast for fieldwork has complex carbs and some sort of protein to keep me going through unpleasant weather and long hours. Ideally, I get a big bowl of oatmeal with nuts (and maybe some brown sugar), some sort of protein (whatever egg thing is available or a dairy product like cottage cheese), and a piece of fruit.
I can work with less ideal conditions when I'm traveling, such as continental breakfasts: some sort of whole-grain cereal without a lot of added sugar, maybe some granola with nuts, and whatever fruit they have buried in the back (old bananas?). But I was recently stumped by a hotel that had nothing but sugary stuff: froot loops and frosted flakes for cereal. "Maple & brown sugar" instant oatmeal (I used to eat that stuff, but either the formulation changed or my taste buds did, because it's way too sweet for me now). Frosted danishes. And even though the hotel supposedly had a hot breakfast, the only thing they had ready by the time I had to go was their signature frosted cinnamon buns. I did eventually find some non-sugary breakfast items: hard-boiled eggs in the dairy case. Whole-wheat toast hidden behind the danishes.
I think that part of the problem was that this hotel catered more to tourists. And when you're on vacation, it can be fun to eat junk food for breakfast ("look, honey - fresh warm sticky buns!"). But when I'm traveling for work and staying at a hotel, this is part of my life. I can't eat that crap on a daily basis without some serious consequences.
I know what you're thinking: geez, just buy some healthy breakfast stuff and keep it in your room already! But my options are somewhat limited if I don't have a fridge/microwave and I don't want to turn into a granola bar. Also, I'm a cheapskate.