I'm looking for the Spanish equivalent of "bon voyage" but don't want to say "Via con Dios" because my friend isn't religious. Is there a more secular way to say this'
Thanks to Vivian and Ricardo, my friend is on her way with a "buen viaje."
As a note it wouldn't be "via con Dios" but "vaya con Dios"
If your friend was not religious but knew you to be it would still be ok to say that. But it is a bit old fashioned like most religious things which have less currency in this new world.
The non religious and more modern form is, as Vivian said, "buen viaje" or more fully "que tengas un buen viaje"