I am a nurse in the NICU and we have gastroschisis babies all the time. I can tell you that your baby will have surgery either right away or within a few days after birth. Your baby will not be able to wear clothes at first because of the surgical incision and other IV's and wires attached to your baby until your baby is stable and healed from surgery.
Helpful things you can bring for your baby are special blankets that you can decorate your babies bed with. Fuzzy fleece ones are not the best ones. Although they are cozy, babies tend to get hot in them, and also newborns like to be tightly swaddled and you cannot do this very well with the fuzzy thick ones. The NICU will supply you with bottles, and should set you up with a breast pump if you plan on breastfeeding. Your baby will not be able to eat for a few weeks if not longer, the average being 21-40 days before being able to eat after surgery from gastroschisis. But if you pump, you can freeze all your milk so its ready for your baby when he/she starts eating. I know that many days seems like a long time, but your babies intestines need to heal. If you have a special stuffed animal, usually you can place that near your babies bed as well. The hospital will let you know once your babies born and in the NICU what you can bring for your baby. Don't forget your camera
So for your bag, mostly pack stuff for you, and a few blankets for your baby is enough at first. Be sure to bring enough clothes and personal items to last you a while, since you live far from the hospital. I am assuming you will be staying somewhere close to the hospital while your baby is there, so you won't be home as often.
Good luck to you, I wish all the best for you and your baby