Whether you are at home or on vacation you can squeeze in these exercises only using your body weight.
1. Superman exercise: lie flat on your stomach with your legs straight and your toes pointed away from your shins and arms outstretched over your head. Next, exhale, contract your abdominal and core muscles stabilizing your spine and slowly extend both hips (raising both legs) a few inches off the ground. While doing this simultaneously raise your arms a few inches off the floor. Make sure to keep both legs and arms extended to avoid rotation. Hold briefly (10-20 seconds). To come back to the starting position slowly let your legs and arms come back to the ground. Make sure to inhale when coming back to the starting position. Superman exercises are good for working the back, butt/hips and shoulders.

2. Push-ups: an oldie but a goodie. The regular push-up works the arms, chest, and shoulders. A standard push-up exercise starts lying on the ground palms flat on the mat or surface with the legs stretched behind. Then, slowly bend your body towards the floor keeping your head and torso aligned with your spine. To finish the push-up press upwards through your arms keeping your body aligned. 10 reps at a time is a good place to start.

3. Front Plank: start flat on your stomach with your forearms and elbows closely at your sides and directly under your shoulders. Slowly lift your entire torso off the mat or ground (keeping your body stiff) and avoid arching your back. Make sure to keep your shoulders positioned over your elbows and hold for a specific amount of time, 5+ seconds. Slowly lower back to the ground at the end of the time. Doing the front plank works the abs and back.

As with any exercises if it starts to hurt or feel uncomfortable stop the exercise.