A good one is to sneak up behind the person who is taking the picture of their friends and/or family with members of our group.
Most people feel rather secure, because they know the action is in front of their camera.
You throw them completely off the track if you just stand behind them, waiting for the photo to be taken and then "control if they did it right".
Instantly they themselves become the focus of attention, much to the enjoyment of the others ...
Walking goofy and clowning around depends on the situation.
If I stand around too long i get bored and need to do something differently.
If there are smaller children I already have found myself doing silly dances with other cartoon walking acts.
If the audience is more mature I walk around as if I own the place and then all of asudden break character and photobomb everyone who is not quick enough to get away.
I also controlled popcorn and fizzy drinks for "imperial standards". (BTW, don't try that without costume!)
So it all depends on my surroundings.
But honestly, I see it as our duty to spread fun in a charming way and for me nothing is more boring than standing around doing nothing.