As others have said, business casual unless you're paying your own way on SWA. Nonrevs often get seated in the same area so you who knows who you might be next to. Don't wear a suit on the plane.

Other than that, just be polite to everybody...nobody expects an applicant to know nonrev/JS etiquette.

Everybody who is from out-of-town probably stays at the company hotel, including interviewers, sim instructors, pilots in training, pilots on overnight, etc.