My SS has a problem with taking things that arent his.  He has done this since he was little.  His mom passed away at 4 years old and therapists think its a learned behavior from the trauma he went through early on.  But this is something he has always done.  If we go out to eat and all order waters he will go refill it with soda.  He loads his pockets with sugar packets and free candies at the door.  He shows up after school with shoes, hats, tumblers, perfume, necklaces, watch, hoodies etc. He has claimed his friends gave stuff to him but we found out on several  occasions he was lying.