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Costumes are mandatory, and can be both elaborate and incredibly simple.

You are your own character in a dive bar in a galaxy far, far away. 

That could mean aliens or creatures of all species and sorts - smugglers, pilots, gangsters, bounty hunters, criminals, etc.

Think vests, khaki, jackets, ponchos, capes, straps, goggles, etc. A lot of looks you'd see in a Western would work. Wasteland gear works. Playa gear is perfect, and so on. A dash of face paint, an alien hair style. Earth-toned desert garb is simple, and a little goes a long way...