Hmmm, that's a tough one, I guess. Not really that hard if you're doing the carb-up during these heavy work hours, though. You can pack the foods you need in a little sack. Protein shakes with added dextrose for the carbs are easy to make ( I put whatever dry mix in seperate bottle and mix into koolade or green tea right before I drink at gym). Zip lock bags of cereal, crackers, bagel, whatever, stuff like that.
I guess tougher if you're doing you ketogenic days on heavy work days!