It's a woody plant, but without anything for scale it's a bit difficult to judge size. It looks to me like an oak with the white part being the two parts of the acorn (acorns are like bean seeds in that they have two parts.)

You can see the corner of an eight and a half by 11 piece of paper in the upper right hand corner. The sea does look a bit large to be an acorn. The scene might be about the size of a walnut in its shell.

Oak

Hmm, has to be an ambitious squirrel storing supplies.

In mos of New England the only common trees with seeds as big as a walnut would be...walnut, oak, hickory, maybe chestnut. You have any of those near you? Anyway, apar from oak, the others all have compound leaves.

The half shell resembles half of a black walnut shell.