Another easy peasy road trip art option is to (A) cut and collect clippings of headlines and quotes and assorted bits from magazines and newspapers; and (B) use a glue stick to randomly add the clippings throughout your art journal.
I carry a #10 envelope and a accordion file folder in my art tote to file my clippings. I put the small bits in the #10 envelope and the bigger pieces in the folder. I don't necessarily use everything I clip on any given trip, but they roll over and go with me on future trips. I often don't remember exactly when or where a clip originated but ultimately they funds homes in my journal pages.
Often the clippings will get buried under many more layers. I generally top with clear gesso (not whole in the car) so they're ready to top with virtually any medium.