If I have to pay attention to the capacity of the lens care bottles (100 ml maximum), nothing prevents me from flying with my contact lenses and to slip them into my luggage.
With a lens case and a clear plastic bag, there's no doubt that my lens kit will go through customs!
Of course, depending on the destination, it is better to be careful and to check the expiry date of my lenses because I may not be able to find some abroad.
If I wear monthly replacement lenses, a second pair of contact lenses will not be too much. You never know, who has never forgotten belongings in the bathroom of a hotel room?
Moreover, daily lenses may be preferred for travel because no lens care products are needed for them.