Hit the hay
Go to bed.
The term hay was used in the USA to mean bed since the early 20th century; for example, from People You Know, by the American author George Ade, 1902:
"After Dinner he smoked one Perfecto and then, when he had put in a frolicsome Hour or so with the North American Review, he crawled into the Hay at 9.30 P.M."
In 1902, mattresses were often sacks stuffed with straw or hay (hence the similar phrase 'hit the sack').
The phrase 'hit the hay' seems to have originated in the US sports scene. The Oakland Tribune, July 1903, reported this:
"'Sam' Berger, the Olympic heavyweight ... was sleepy and he announced that 'he was going to hit the hay.'"
In 1905, Paxton Sport USA included this:
[the baseball player] "has a language of his own. Going to bed for him is to 'hit the hay.'"