There a few bodyweight exercises I like to do on my off days from the gym. They are great for when you're on vacation or staying in a hotel too! Not necessarily good if you have a glass office though...
I usually combine the regular plank with side planks and variations of lifting limbs up off the floor at the same time. I remember BARELY being able to hold a regular plank for 30 seconds when I started strengthening exercises 3 years ago, now I'm going for at least 4 minutes at a time. It is the perfect workout for your entire body, from your neck to your calves.
I do these 2 different ways: my back on the wall and my legs bent at a 90-degree angle, holding for 4 minutes or so, or facing the wall and doing regular bodyweight squats, making sure I'm as close to the wall without touching as possible. This is also a great way to work on your squat technique.
I do mine against a wall or closed door. Handstands are my least favourite, but also the strengthening exercise I have most improved on. My trainer used to have to lift my feet up and position me because I was so weirded out by being upside down. Now I cartwheel into them! Handstands are the best way to strengthen your shoulders, in my opinion. I wish I could hold them for longer than a minute, but I feel like I'll pass out if I go a second longer.
SOMETIMES I'm able to balance mid-air. Sometimes.
TD and I have committed to working out while we're in Playa. You know, to balance out the lime margs we'll be consuming. Do you workout while on vacation?