A little additional EMH info...
For AM EMH everyone in your party will need to have their KTTW card (aka "room" key) to get into the park early - that's assuming your park keys aren't on your KTTW already.
For PM EMH you will each need to show your KTTW at the entrace to any rides/attractions.
Exception to both is very young kids who aren't usually issued KTTW cards. Also for PM EMH, more often than not younger kids aren't asked for their cards if they're with adults/parents.
PM EMH is a little different in that Disney allows non-resort guests to stay in the park and eat, shop, hang around - although they can't ride without valid KTTW cards.
For the hard ticket parties (
MVMCP and
MNSSHP) ticket holders are issued wristbands and CMs check for them throughout the park as well as at ride entrances, stores, restaurants (I've even heard restrooms!) after the official start of the party. People without wristbands are nicely pointed to the exits and told they need to buy a ticket if they want to stay.