You should file a document called RTA(Request for Travel Authorization) before you travel. After you return from your trip, bring your receipts to Stacy and she will reimburse you. For major receipts (like registration, airfare, hotel) the receipt HAS to show that it has been paid by one of these methods:
1) a receipt that says 'paid'
2) a credit card receipt
3) a receipt that shows a credit card was used (there is usually some indication on the receipt if you know what to look for)
4) a receipt that says 'balance due: 0'
for a taxi receipt it doesn't have to show payment was made. If you will be being reimbursed for food, food receipts are not needed at all.
You can fill out your RTA on-line or you can pick them up at the accounting office. In either case you will need to come by the accounting office and pick up some other forms you'll need to fill out (they are not on-line).
Even if you are not going to be reimbursed from the department since you got travel money from the conference organization, you still need to file the RTA form.