If you are staying at the Venetian then a trip to the Bouchon Bakery is a must. As others have mentioned it's tucked away under an escalator near the main elevator banks for the hotel. Another has opened on the street between the Venetian and Palazzo on the Venetian side.
The ham and cheese on french bread grilled with mustard is pretty tasty as a lunch option. Mango yogurt is nice for breakfast, be warned definitely on the sweet side. The baked goods, like croissants are great as is their coffee.