The simplest exercise a trucker can do is walk. Walking 30 minutes everyday will help us in many ways. If, you want to keep a simple routine, choose walking. I would encourage you to add a few 
things. Some resistance training can help strengthen your upper as well as your lower body. You don't necessarily have to go to the gym and try to max lift. Using a few resistance bands in your truck will help. The Freightliner In Cab Training (FIT) system can give help your core in about 10 minutes per day. Doing the front hook portions of the workout one day and the sleeper hook portions the next day make the workouts quick and easy.
The more different things that you do, the better off you are. Look, I realize that while we are in a truck our choices are limited. Simple matters. Quick matters. Ease of clean up matters. I keep a stash of clean up supplies in the truck. Those include baby wipes, baby powder, a good waterless hand cleaner, and deodorant. These are good, but they don't replace a shower. I like to run in the morning, near the end of
my 10 hour break. Sometimes, I can do this where there is a shower. Sometimes I can't. That is when the alternative clean up comes into play.
A bike is a great thing to have in your truck. Riding a bike seems more like playing or using alternative transportation than exercise. It is exercise. When you're home look for other ways to exercise. Kayaking has become my favorite alternative exercise. I live in northeast Wisconsin. Water freezes there in the winter. I do use my motorcycle rain gear to expand the season, but alas the kayak makes a lousy ice breaker. Cross country skiing is a great winter exercise for me. These are just examples. They might not work for you. Do what works for you. All exercise works, when you do it.
The fit bit craze is a mixed blessing. It encourages us to take a few extra steps, and maybe park in the back row at the truck stop. That is a good thing. If it becomes a way to not set aside that 30 minutes a day, it is a bad thing. All exercise is good. Walking for 3 minutes when you wouldn't walk before is helpful. Remember that the body builds up to a higher metabolic rate. You get the most out of your exercise during the 20-45 minute range.
The Olympics will be starting soon. Watch them. Root for the USA. These athletes are inspirational. Lack of motivation ends more exercise lifestyles than anything. Grab motivation from anywhere you can. Remember that their goals are different than ours. They are training to be great at one thing for a specified period of time. We are looking to get healthier for the rest of our lives.