Personally, I plan my meals around the expected temperatures of the day.
Here in FL, it's not unusual to have temperatures of 40-ish in the mornings in the "winter" and in the 80s with 100% humidity in the summer mornings. So, my breakfast varies.
During the summer months, I tend to carry peanut butter espresso fudge; this is the bog-standard Fluff recipe with an half-pot of Cafe Bustelo added to the mix. It doesn't melt at normal FL summer temperatures, has enough sugar and fat to boost one's calories in the morning, contains the caffeine that I'm addicted to, and--most importantly when it's that warm out-- doesn't require me to wait an half-hour for it to cool down before I can eat it.
During the cooler months (when it's below 70 in the mornings), I tend not to eat breakfast bars; instead I use a melange of instant coffee, Carnation Instant Breakfast, and Nido (whole milk powder). If I were to eat a breakfast bar, though, it would probably be Pop Tarts of one flavor or another.