In keeping with a long tradition of ship's cats, Jonesy is the Nostromo's cat—a ginger tom to be precisely precise—and he lives his life by the words of one of the great philosophers of our day, Gloria Gaynor.
Yes, this little guy is a survivor. Other than Ripley, Jonesy is the only member of the crew to live through the alien's kill-a-thon, but why? He comes face-to-maw with the alien twice that we know about. During the last encounter, the alien has the cat cornered in a storage box and still leaves him alone.
Does the alien simply not perceive Jonesy as a threat? Does it see the cat as compatible with its natural order, whereas it views the human crew as an invasive species? Maybe it's just saving Jonesy for a snack once it has finished the main course? Depending on how you answer this question, it could lead you to some interesting ideas on the alien and the theme of man and the natural world.