Coolness is all about swag. If you have swag, other kids will notice you. To build swag, you'll need a baseball cap. You can wear it forwards or backwards. Just don't wear it like Clyde. He wears his cap like he's going to a baseball game.
Next, you'll need a cool shirt and a hip walk. Your walk should be unique and cool. If you walk like Jerry, you'll be very cool.
PACK LIGHT. PLAN TO SHOP.
Shopping is a great way to immerse yourself in the culture of the places you visit. Along with your free day, I also recommend packing one-too-few days worth of clothing. Treat yourself to a lighter suitcase on the way there, and a new/local outfit as a wearable memory.