Here's what I do: if the place I'm going to has a piano, I would practice on the piano, if not, I'll practice on the table.
In this case, I mentally imagine the sounds of the pieces in my head and depress the virtual keys with my fingers on the table and virtual pedals with my feet on the floor.
Not for a moment must I forget this is a real organ practice and use the same principles as on the organ - keeping heels and knees together, keeping fingers and feet in contact with the keys and pedals etc.
This kind of practice is very flexible, you can do it even in a hotel room with some pillows on the chair to adjust its height.
Yes, some less essential elements of organ practice can be postponed when you're traveling but I don't recommend skipping organ practice altogether, especially if you are on a deadline.
PS If you don't have a deadline (real or invented), you can't hope to achieve much in organ playing.
Transposing Sequence in B Minor: i-vii65o-i6