At 18:10 Regina says "I don't care if they're dancing daffodils." This is possibly a reference to Alice in Wonderland (1951) and the singing/dancing flowers. More likely, though, it is a reference to the 1932 Silly Symphony "Flowers and Trees" which features daffodils dancing around and along with trees.
When Killian is talking to Henry by the yellow Bug, there is a box van behind him with a logo that says "Game of Thorns". This references Game of Thrones which started running the same year as Once Upon A Time. It is the name of Belle's dad's flower shop in Storybrooke.