Oddly, the first picnic that occurred to me (other than Emma, and that's been covered) was the one in At Home in Mitford, in which Father Tim takes Cynthia out on what he hopes will be an enjoyable and possibly even romantic picnic.
Unfortunately for Father Tim and his plans, a bull decides to crash the party.
I really love the Mitford books. They are as sweet and cosy and comfortable as the title, and manage to focus heavily on Christianity without coming off as preachy. (And as I'm not Christian, that's not a biased opinion.)
If you're looking for a fuzzy, comfortable, comforting read, give them a try.