Halloween isn't such a big deal in Europe (at least in France), so I've never really dressed for that event. However we do have Mardi Gras, which has nothing to do with the US celebration but the name. Last time I participated was somewhere in 1997, maybe 1996? I was 8 or 9 years old ...
I've done a lot of costuming though, I've been involved in theater plays my whole school life, from 6 to 18 or 19 years old.
I don't have the time nor the money right now to put together a proper Star Wars costume, but if I could, I'd most likely go as an ARC Trooper.
I'd get the armour, get the paintings needed to make it "camouflage", would create dents here and there, weather some parts of it, would probably add some black stick lines on the side of the helmet or on the inside of the arm, as a way to count the victims I made or how many clankers I reduced to pieces.
Maybe put a lightsaber to my belt, as a way to either symbolise the elimination of a Jedi Master during Order 66 or the exact opposite, being the safekeeper of it until this whole mess blows over (and a pint over at the Winchester
)
I'll need to convince the wifey though ... As I'll need her help (she's a much much better painter than I am)