With hydraulic brakes, when the wheel is out of the bike you need to ensure there is a spacer inserted into the calliper. If it is not, and if the brake lever is operated, the brake pads come in close together and the wheel with the disc can’t be refitted. This is not the end of the world and gentle prizing apart with a few flat screwdrivers will do it.
Whilst disc rotors are not particularly vulnerable (and can to an extent be straightened if bent), it is recommended to still take special care of the rotor when putting the bike into a bike rack or packing it for travel. This is no different to taking care of a rear derailleur. If it sticks out then protect it.
Always travel with a spare set of pads. Be familiar with how to replace them. It is very simple.