"Joke" (rice porridge) with fixins (pork, egg, etc.) is probably the number one traditional Thai breakfast dish. After that dishes like chicken-rice (Khao Manh Gai), noodle soup (guway teow) and the national dish of Thailand (sorry Field Marshall Phibun) stir-fried pork with rice and a fried egg on top (Pad Kra Pow Moo Kai Dow) seem popular for breakfast, and mid-morning snack, lunch, mid-afternoon nosh, early supper, dinner, late dinner, midnight snack - the lucky number 8 for Thai meals. Can't speak to the country folk but city folk are becoming a bit more westernized so bread/toast/waffles/yogurt are popular with city workers. The Thai omelet (Kai Tcheeow, with pork, moo saap) is really more of an accompaniment with a traditional family style dinner; often paired with Tom Yum Goong, than a stand-alone breakfast dish.