Becasue so many times the vouchers never get to the guest, when arriving at Orlando airport any evidence of your ME reservation should do. According to anecdotal evicence, despite the chagrin of taxi drivers, if push came to shove, the guest with any Disney resort reservation has been allowed on ME. At least get the name of the person you talked to on the phone if you had had to discuss ME changes or irregularites before your trip.
The vouchers are needed for the return trip. If you never got them, you can have new ones made either at the airport or at the resort. Be sure to get a bus time for the homebound trip too. This time should be about 3 hours before your flight leaves, ask for an even earlier departure if you also want to get food at the airport.