Depends on how serious about it you are. If you want to do serious weight training, in the body-building direction, you are going to need to bid overnights that have real gyms nearby. I know one guy who does this...I tend to plan my workouts based on where I'm going, but if I see this guy on my schedule I plan on serious weights for a few days.

If you just want to stay fit and toned, do most of your weights at home, and focus on cardio and calisthenics on the road. There are a variety of systems such PX90 that people use to good effect. Many hotels have dumbbells up to fifty pounds, which covers a lot, but not all, of my arm stuff.

I keep a spreadsheet of all our hotels, which includes detailed gym info so I can plan accordingly.

As fas as diets...you either have to pack it or keep a list of local stores/eateries which cater to what you want to eat, and bid accordingly.