Remember to pack your bags light.  Everything you need will be provided for you by OCS (in your small and large kit bags).  You will be carrying your bags around for a couple days until you are settled and this is why it is important to pack light.  Insure your bag is sturdy because often the straps break and the candidate is left without any efficient means to move his gear about (A funny experience, but not when it is you!). 

It is also important to mark your gear before arriving because it is often mixed up during the confusion of in-processing.  Zip lock bags come in handy and can be reused in later training evolutions to protect items from water while in the field.

When packing make sure your toiletries and  running shoes are easily accessible.  You will need these most often during the time you are living from your luggage.