Naturally, enough, what you should consider to cook and prepare for a picnic depends on your definition of a picnic. Here I am specifically referring to food eaten away from home, having been carried to that remote spot.
For recipes for eating outside at home (al fresco), including barbecues and lawn picnics, see here.
Throwing a few sandwiches into a rucksack and setting off for a day's walking in the hills of the Lake District. For this style, take plenty of bottled water and make sure that everything will not get damaged by being squashed or getting just a little wet.
An organised picnic for family or a small group of friends, sitting on a blanket in a sunny field somewhere a fairly short walk from the car. Take prepared salads, fresh fruit, crusty bread, and a good selection of hams and cheeses, and perhaps a small bottle of red wine? A traditional wickerwork basket is definitely a plus.
A grand picnic for a large number of guests, with trestle tables and linen tablecloths. Eat boned and rolled turkey stuffed with ham, carved at the table, with silver service vegetables. Serve champagne in cut glass flutes. A small army of servants is mandatory.
Needless to say, it is the second scenario which I am targetting here. Picnics which can be prepared quickly, with fresh food and fine wines (or beers) - definitely picnics for men!
Mind you, I have certainly done my fair share of stomping up the hills of Scotland, and indeed other places in my time. And I have even catered for the grander event, for our table at an Edwardian-style picnic many years ago.