U
Ugg boots : Australian sheepskin boots worn by surfers since at least the 1960s to keep warm while out of the water. Also worn by airmen during WW1 and WW2 because of the need to maintain warmth in non-pressurized planes at high altitudes.
Ugh : ugly. hence Ugg boots
Uni : university
Unit : flat, apartment
Up oneself : have a high opinion of oneself - "he's really up himself"
Up somebody, get : to rebuke somebody - "the boss got up me for being late"
Useful as an ashtray on a motorbike / tits on a bull : unhelpful or incompetent person or thing - "he, she or it is about as useful as tits on a bull" etc. etc.
Ute : utility vehicle, pickup truck
V
Vedgies : vegetables
Vee dub : Volkswagen
Veg out : relax in front of the TV (like a vegetable)
Vejjo : vegetarian
Vinnie's : St. Vincent De Paul's (charity thrift stores and hostels)
Don't forget to take my address with you, cuz you'll need to write it down on your Customs Declaration.. aaaaaaaand they may ask you when you're checking in!