The easiest and most accessible exercise no matter where you are is walking. To make it a little more challenging, you could walk around carrying your backpack or luggage. The added weight will increase your heart rate to something higher than normal and will make sure you work that much harder and burn more calories. You should also try and run whenever you can.
If you’re travelling and find yourself staying in hotels, make sure to check if they’ve got a pool. Swimming is a safe and quick way to get in some exercise and keep yourself fit and toned.
At home, some easy to do workouts would be something like push-ups or burpees.
Lastly, just relax. If you’re travelling a lot, it is only normal for you to go off-track. So, don’t spend too much time worrying about it. Focus on getting as much sleep and nutrition in as your circumstances allow at first.