It really depends on the situation. For example, are you the person's landlord, or just a friend? If you send them a notice and say you will throw it out/donate it in 1 month if they don't pick it up ... then you probably should be ok. Or if it was your ex, say, and they left a few shirts/shoes/whatever, and it's been a month already, tell them to pick their stuff up or you'll throw it out. If someone leaves something at your house, and never makes ANY contact with you or ANY form of wanting their stuff back, then give them one final chance (in writing is best) and then throw it out. As per any specific laws about this, again it depends.