Bring a change of clothes for him, too; he won't want to sit in the same outfit he came in, especially if your labor lasts for more than a few hours.
Tote a book or a magazine for him to read while you're laboring. (He'll thank you later.)
A toothbrush, toothpaste, and other basic toiletries for him will freshen and cheer him up for your big moment, even if he's been up all night long.
Bring at least 20 dollars in cash and change for snacks, phone calls to family members, and any of your miscellaneous cravings or whims.
Make sure one of you has a watch with a second hand, so your husband can time your contractions. He'll be able to tell you when your next one is coming, calming you down.
Be sure your partner has a cell phone when you head to the hospital. He can call friends and family to update them on your progress -- and announce the big news when Baby arrives. (Be sure to pack the charger as well!)
If your partner spends the night with you at the hospital, the staff will bring in a cot or turn down a reclining chair in your room. Bringing his own pillow from home can go a long ways towards helping him be more comfortable (and better rested).
More and more hospitals have Wi-Fi in birthing and recovery rooms. Call ahead and find out if yours does as well -- if so, packing a laptop can help you and your partner stay in touch with friends and family.