Acorn

Acorns are items only found in Click Clock Wood in Autumn. There are a total of six acorns that must be collected and given to Nabnut, which he will eat so that he does not starve during the Winter. If all six acorns are given to Nabnut, he will award Banjo and Kazooie with a Jiggy.

Trivia
Although Nabnut is seen eating a pile of acorns in the Summer, he only needs six of them to survive through the Winter.