^^^This. You are not guaranteed to get into the park if you have a ticket. If all the slots in one particular park are taken for that day, you won't be allowed into that park, even with a valid ticket. You would have to try a different park. And if all the passes are given for every park for that day, you won't get in. It's best to reserve in advance. I'm not sure whether or not you are allowed to switch the passes for a different park after you've reserved...anyone else know? Like...if you reserve for MK for a day but then decide you'd rather go to AK that day, can you switch them?