Here's a list of five things that you should not step out of your office without once you are told that you are being laid off:

Layoff letter: Be aware of the reality that you may not find a new job soon and that you will need some money in the interim to tide your out. Hence, ensure that you ask your boss to provide you with a letter stating that you are being laid off. Further, if your being laid off because the company's new products are not doing well and hence the company wants to cut costs in order to minimize losses, ask your boss to state that in the letter. Such a letter would have two benefits: One, you can submit this letter to your local unemployment bureau and speed up the processing of your unemployment benefits. Two, you can show a copy of this letter to prospective employers to prove that you were not laid off because of performance issues.
Your last paycheck: Do not leave with collecting your last paycheck and ensure that it covers remuneration for all the days that you have worked and for all the unused paid time off. This is mandated by the law and hence you company cannot refuse your request. However, if they need a few days to process your payment, ask them for a letter stating the same and make sure that they put in a date as to when you can expect your check. If you do not take care of this formality, you may go crazy chasing the accounts department for your money, and you definitely do not want that additional hassle. Further, ask whether in your settlement paycheck, they would be accounting for any of the bonuses or pay increases that you are entitled to. After all, there is no harm in asking, is there?
Your COBRA information: It may be some time before you get a new job, and in the interim, you may want to be covered for insurance and hence apply for COBRA. So, make sure that you have accurate COBRA information with you prior to leaving the office on that last day.
Letter of Recommendation: If your boss is sincerely apologetic for having to let you go, ask him if you can cite his as a reference. If he agrees, ask him to write you a letter of recommendation letter then and there. In the letter, request him to detail your workplace performance and state that you were not let go because of poor performance. You could even maybe request him to add you to his LinkedIn network and provide you an online reference on the site.
While these five things will not reduce the pain caused by your lay off, they will definitely go a long way in help you come to terms with it and get on with your life.