The website that sells the Master's tickets explains that the dress code requires appropriate shoes and clothing at all times. Being that this is a golf tournament, appropriate would cover any type of clothing you would wear if you were actually playing golf. For those that don't play golf, a collared shirt and khaki pants are ideal. Since it will most likely be a hot day, khaki shorts are also acceptable. Make sure your pants don't have extra pockets or are too baggy. Two pockets on the hips and two pockets on the back is normal. Denim of any sort isn't allowed.
Golfers wear golf cleats while playing, but spectators aren't expected to do the same. Spectators are recommended to wear comfortable walking shoes for the tournament. Boots or heavy shoes are rarely worn and only a few people elect to wear sandals. Many dress in golf clothing with golf shoes out of respect for the the game and its players.
There is a long list of things that will be prohibited from the tournament. Even if you're dressed properly, you won't be able to bring certain items, such as cell phones, bags, backpacks, purses, cameras, alcoholic beverages, flags, banners, signs, folding armchairs, radios, strollers and walkie-talkies.