I tried several workout programs over the last six years.
My favorite program is based on weight-lifting exercises. I like free weights because sessions are short, efficient, and straight-forward. Short sessions easily fit in a day, the endorphin high is extremely valuable to my work. A combination of squats, dead-lifts, barbell rows, overhead presses, and bench presses cover every muscle of your body.
Living as a digital nomad, I am also forced to adapt to my surroundings: I can't always get access to a gym, and I can't always do the same exercises depending on the pieces of furniture available in the places I rent. Body-weight programs are longer yet minimalist. Pull-ups, squats, and push-ups are incredibly versatile. The learning curve is also lower than barbell-based exercises.
In both cases, sticking to a workout routine is not trivial. To avoid this problem I just set a simple rule for myself: DO IT EVERY DAY. I'm not saying you should hit the gym at 100% intensity every day, but it's easier to stick when you remove all means of escape: split routine for the win!
Stretching is another thing you might want to do every day. It's good for your health, and good for your mood. It also forces you to have a quick warm-up right before: more exercise can't be bad.