Can anybody explain what a huckleberry picnic is? I've found lots of quotes but none of them defines the term:

"But at a huckleberry pic-nic, we had a better appetite, even, than usual."
--from A Budget of Willow Lane Stories by Francis Channing Woodworth, 1852.

"...when, suddenly surrounding the top of the mountain, they captured a place where some of your boys and girls had been having a huckleberry picnic; and that was all they ever did find."
--from American Bastile: A History of the Illegal Arrests and Imprisonment of American Citizens during the Late Civil War by John A. Marshall, 1869.

"When I was fourteen and Nelly was eleven we went one day to a huckleberry picnic."
--from More Bed-Time Stories by Louise Chandler Moulton, 1875

"Guess yer bin on a huckleberry picnic from the looks o' yer togs."
--from "A Difficult Trust" by H. S. Atwater, Chapter XIV, in Arthur's Home Magazine, December, 1885.

"...I hasten to a pest-hole of diphtheria with the same joyous alacrity that I would drop in on a Dutch dance or a huckleberry picnic."
--from Transactions of the Minnesota State Medical Society, 1885.

"On Saturday last 'Oak Grove Creamery,' in the suburbs of the city [Boston], gave five hundred newsboys a huckleberry picnic."
--from Unity. Vol. XXI, No. 24, August 11, 1888.