One of the most important thing they should tell new parents is to label absolutely everything that is not on your child's body, including coats, hats, shoes, anything they may remove.
It rained heavily during the first couple days of school this year so Lee wore his new yellow rain slicker that he is in love with. When I went to pick him up that afternoon, the teacher greeted me with a most apologetic look on her face. "I'm so sorry, but we accidentally gave his coat to the boy he shares a cubby with", she said. The perfect storm of circumstances lead to this unfortunate mishap that left my child with no coat to wear home in the rain. The other boy was picked up early that day by someone who was not his mother or father and couldn't have known that he did not own the coat. The teacher handed over the book bag and coat thinking it belonged to the right child. The other child's name was in his coat, but Lee's name was not. I guess there was some confusion as to who was who because the wrong coat was left behind for Lee. It was an honest mistake but try explaining that to a 3 year old who is just getting used to a new situation. It was not pretty. Luckily, by the time we got outside the rain stated to hold up so he didn't get very wet at all. The coat was returned the next morning and all was well.
Since then, I've learned to put his name on absolutely everything that is not attached to him - clothing, sheets, blankets, pillows, utensils, etc. I use the labels from Name Bubbles and they're great. I especially love the shoe labels because they have a plastic protective cover that keeps the labels in place.