1. Walk along one of the two harbours (La Condamine and Fontvieille) and watch the beautiful yachts (though for me a boat can only be beautiful if it has a sail), then turn around and count luxury cars.
2. Watch the changing of the guard twice a day, in front of the Palais Princier on the top of the rocky hill called Le Rocher then walk in the old streets of Monaco-Ville
3. Gamble at the Casino, or more likely take pictures in front of it. If you want to spend a lot of money, just buy an espresso at the Café de Paris
4. See exotic fish and plants: Go to the aquariums at the Oceanographic Museum and/or to the Exotic Garden.