Which toys do you let your toddler take down to the play area?

My son is a year old and has decided that anything he carries downstairs belongs to him alone. Another child touches his ball and he screams. He picks up theirs, of course, and is astonished when they want it back. I think part of the answer is leaving his favourites at home so there's nothing precious to guard. But then what do I take? Do others keep a separate set of 'outside' toys that nobody minds sharing?