When sending packages overseas it is best to send them Priority Mail. They will get there much faster than Parcel Post because they will be flown rather than sent by ship.
By going to USPS you can get free shipping materials. They will deliver Priority Mail materials that you order at no additional cost.
As of April 2008 a new larger flat-rate box made specifically for care packages was made. The shipping is $10.95 to a military address. This is a $2 discount from the regular shipping.
Average shipping time to Iraq is around 2 weeks. Keep in mind that once the mail is on base it takes some time to distribute.