Work travel sometimes seems to be all about food. It's not always particularly good food, but there's an endless round of lounge food, hotel food, sandwiches and cakes, breakfast meetings and lunches, dinners with colleagues...
Sometimes by the end of a three or four day work trip I feel like I've eaten so much I might bring the plane down!
There are a couple of thing I've started doing to try to avoid feeling like a sluggish sloth after a work trip.
First, I take my breakfast with me. I like eggs for breakfast, so a couple of hard boiled eggs in an insulated lunchbox with a reusable ice block (like the ones you use in an Esky), plus some fruit snaffled along the way somewhere (or when traveling to a state where they're serious about quarantine, I pop into a supermarket) and my travel plunger (French press, for our American friends) and a mini bag of coffee means I get a satisfying breakfast with enough protein that I don't feel tempted to binge mid-morning. If you eat cereal, even easier - and most hotels will bring you a jug of milk to your room if you ask for it for your tea/coffee.
Second, I try to go for a swim. My bathers, goggles and swimming cap fit neatly into a medium sized Eagle Creek pack-it sack - http://shop.eaglecreek.com/packit-sac-medium/d/1098 - they're water resistant so stop my bathers getting everything wet once I've used them, if they don't have time to dry.
A zip-lock bag would probably also work. What doesn't work for me is carrying sneakers and gym gear - it just takes up way too much space in my bag, and since I'd prefer to do pretty much anything other than waste time waiting for luggage - especially when Qantas premium tags seem only to work on a random basis - there's no way I'm checking luggage. So a swim is exercise I can do without packing a heap of stuff.
I'm currently sitting in the Qantas lounge in Brisbane on my way back from a two night stay, and despite a full schedule I managed to swim both days, so I'm feeling good about the exercise and less bad about the chocolate brownie I just ate!