Looks like Rob was with Kristen's bodyguard. Here pictures of her with him at the same location - same backpack
Marcus Foster was pictured there too
The caption from the pap agency
Kristen Stewart, Oct 29, 2011: ' Twilight' stars Robert Pattinson and Kristen Stewart are seen arriving separately at an apartment. Pattinson was seen arriving at the apartment on the evening of October 29. A tired-looking Stewart was spotted arriving around lunchtime on October 31 Pattinson's rep Sarah Spear visited the apartment on the evening of October 30.
Thanks to Pattinsonlife/Bigger thanks @shesgotthemoves