Cats --can adapt to many environments and situations and seem , as studies show, to have a physiological benefit to the owner. Cats in fact are so adaptable that they must be hunted in antartica, as they take out Penguins by the truckload. They were left/escaped from the many research stations there and prospered...
Dogs -- This is my Dog, his name is Bitey. Dogs are fantastic animals, loyal and extremely trainable with patience... your vargr crew might get insulted, but thats when you sic the dog on them (hehee)
But please, no Dirty, Evil, Monkeys! Hollywood has made them cute, but look closely! You may as well buy a small evil human, prone to breaking things, flinging crap, and chronically "whipping the Bishop" Sure, you can say "What about helper monkeys?" Sure they help, but only till they find a good chance to shiv ya... Iplayed once with a guy who had a Stateroom for his Beaked Monkey, which was pretty cool, up to the "Monkey" part...
I know you said aliens, but that is one thing about most forms of traveller that can be hard to conjecturize by using the brilliantly general Animal Encounter system. "ohhh! a baby Pouncer!" or "what a beautiful Intermittent you have there!" it lays the groundwork for developing pets brilliantly...
I man lives nearby who has a Helper/Seeing Eye Horse, a small pony that wears custom designed sneakers!
http://www.guidehorse.com/