Any evidence of having made an advance reservation will do for your ride from the airport to your resort. Including yellow Magical Express tags. You do not need to be punctual nor will you be kept waiting unnecessarily if you got there early.
Randomly at the welcoming area they may ask for specific documents. If you don't have the ones they ask for then you will have to stop at the welcoming counter prior to getting in line for the buses.
For going home you need written confirmation of a specific departure time. If you don't get this at your room on the morning of the day before the day you will leave then go down to the front desk immediately and reconfirm this (or make corrections) before heading to the parks. Get the correct confirmation in writing as soon as it is produced including returning the resort that afternoon before the day you will leave if needed. You must be at the DME bus stop at your resort ready to go, children, carryons, etc. in hand, 15 minutes in advance. Suggest planning and replanning your last day so your targeted time back at your resort is an hour in advance.