Just another GR refugee. Other than that, I had a stroke in 2004, and read almost anything I can get my hands on, though I have a particular weakness for history, mystery, and historical fiction.
Maida's Little House.
Well, I don't feel bad about this, as it seems almost everyone is listing "well, I read this book with a picnic in it in childhood..."
Maida's Little House is the second volume of the Maida books, published from 1909 into the early 1950s. They are all by Inez Haynes Irwin, and there are often substantial gaps in publication date; the first, Maida's Little Shop, came out in 1909, but this, the second one, appeared in the 1920s. They are about Maida, the only child of a millionaire industrialist, "Buffalo" Westabrook, and her friends (the "Big Six" and the "Little Six"), whom she meets in Boston. In this one, they all go to spend the summer at Maida's childhood home, in rural Massachusetts. And it has not one picnic, but two!
At one point, the older children (the "Big Six") take canoes out to cross the lake, and bring a lunch basket, so that they can have a picnic on the other side. No one remembers to bring the salt, and it is interrupted by horrible wails, and they flee in terror back to the house. (This is not a scary series; the wails were from a baby. In a cave. Which made them sound very eerie.)
The second picnic is at the shore, where everyone brings salt, and they catch a giant turtle and bring it home to live in the lake. And then realize it needs salt water rather than fresh, and take it back to the sea, to let it go.
I loved all of the books of this series that I had (seven; perhaps half the series) when I was growing up. I had my mother's copies.