Wales is not represented because when the flag first appeared it was already united with England. The design and colours (especially the Blue Ensign) have been the basis for a number of other flags including other Commonwealth countries and their constituent states or provinces, as well as British overseas territories.
National anthem is "God Save The Queen". Each part of the UK has its own symbol:
England - red rose
Ireland – shamrock
Wales - leek, daffodil
Scotland – thistle.