Thanks ladies. I have each time made him pick them up himself but didn't think to make him say sorry. Thanks for the tip. I also made him help put some away. It started off alright and then he got board. Since then I have kept a sharper eye on him and have not let him alone in my bedroom. We don't have doors at the mo so it's a bit of a problem. Anyways, a twist to the story, the last time this happened I found my daughter of 5 vigorously emptying the contents of a drawer on the floor after my son had already emptied my clothes basket, also on the floor. It was like she was trying to get him into more trouble. Was very surprised and disappointed as she had never done anything of the sort before. She's never been a problem except for the constant picking on her little brother. Well I made her pick up everything and put back the contents of the drawer and made her appologise both to me and her brother. So far so good, the incidents have stopped and I'm kind of wondering if my daughter had anything to do with the other past incidents. Anyways I'll keep my cool if this happens again and will go through the whole process though I really hope that this is the end of it.

Actually, he cannot understand your explanation at this age, as you are probably realizing. Not only that, but he has a good intent and a real need behind his actions.
It helps to understand WHY he is driven to do this. Only then you can help. Most often he is just needing a sense of power and play. I played with my children in situations like this and it vanished fast.

Read from page 200 on (or the whole chapter starting page 193) of the book, Raising Our Children, Raising Ourselves. It will show you how to help your child and how to turn the whole thing into therapy and joy.