My dd was an angel at WDW at 6 months and TDR at 13 months. Now, nearly 24 months, we struggle to get through a trip to the grocery store. Be firm, be consistant, and be prepared to bail.
Try to enforce rules consistently, and with the same tone. Today's lectures included:
"You have to hold my hand in the parking lot. It's not an option. We can do this the hard way or the easy way." (Easy way, she holds my hand. Hard way, I grasp her hand firm enough she can't pull away. Today, she decided to hold my hand while we walked through the parking lot, and I allowed her to let go once we were on the sidewalk.)
"Don't touch that rack of sunglasses. You have a pair at home, you don't need more." (I took her hand and led her away from the display rack, despite her protests.)
"You have to stay with me. Don't wonder away, or I'll put you into the shopping cart (or buckle you in the stroller or carry you)." (She followed me through the produce section, but I carried her after she took off in the salad dressing aisle.)
DD has an excellent vocabulary and communicates very well. However, she has a hard time coping with different rules at home versus daycare versus Grandma's house. If we had different rules at WDW, she would be totally messed up.
If we were planning a trip to WDW with her, my wife and I would (or should) have a game-plan about what reaction is appropriate for what behavior, so that we're on the same page when it comes to discipline. And we wouldn't be afraid to leave the parks for a quiet spot in a nearby or our own resort room if necessary. As wonderful as Disney parks are, there's no downer like a wailing toddler at your feet.
FYI, these are my opinions about what works for my child. I don't like to be told how to parent, and I don't want anyone to think I've got the perfect answers.