It's been a while since I last presented at NAEA, but they should have let you know all this already. You purchase the supplies for your workshop and pay for the shipping, and submit your receipts to the Reston office, not at the conference. They will have an address for you to ship to; it will be a warehouse that will deliver your boxes to the conference center or hotel. Call Reston to clarify all this.
Have fun! I miss you guys so much. We always had such a great time at the conventions.