No jackets, ties, caps, no nothing. Just short/long sleeved shirts. They give you a pullover for winter ops and a pair of gloves. Onboard the aircraft are 2 winter ops high viss jackets for the turnarounds. It's not strict, people are relaxed and if you want to wear a jacket you could in theory wear it at an outstation or during deadheads. You do hardly see anyone wearing non company provided clothing though. There is a Uniform Standard Manual for those loooong nights if you do get bored.