You order packages from HQ during missions. While in a mission click on the "C" in the upper left hand corner of the screen. You can then click on what you would like to order. You can order grenades, rockets, health and other things. These items range from 3,000 command points up to 19,000 command points. Once you have everything you would like to order, click buy. The command points will be deducted from your total command points and the item(s) you bought will be dropped with a parachute to your location.
If you are like me, you won't even be close to having ordered 50 packages from HQ by the time you are done with the game. In order to get to 50 packages, you can load up any level, except the zombie areas, and just continue to buy packages until the achievement pops. The speed burst is the cheapest item at 3,000 command points. You will have to buy one at a time, so buy one, pick it up and then buy another one and so on. You will still be able to buy a speed burst even if the previous one is still active.
Thank you for the clarification janiwesterling!