In addition to the I-Spy and Rock, Paper, Scissors games, our children like to look through their signature books and also do the pin-trading. Some of the lines can be "stuck" for a while, and it's good pin-trading time for DD. Sometimes kids will strike up a conversation with another child, too (my DD was 6 during our last trip, but she began chatting with other little girls about their pins or rides, etc.)
Also, a little snack will help re-energize a child while waiting. I try to take small crackers, raisins, etc., - nothing to spoil their meal or rot their teeth - just something to pass the time.