Assuming you can guarantee the weather, (ha!) the key to a good picnic is simplicity. What you don't want is dozens of little pots and containers which then leak, spill or get forgotten; or 3 different cold quiches which all taste the same. The following ideas have all worked well:
-A hot roast chicken makes a lovely picnic lunch, and all you need with it some crusty bread and a few tomatoes. A small one cooks in just over an hour; otherwise, most supermarkets have hot cooked chickens on sale.
-A big, really flavoursome savoury pie, tart or quiche is great, especially if you can keep it warm. Again, bread and tomatoes is all you need – or baked potatoes, foil-wrapped.
-If you take a baguette, scoop out some of the bread and stuff it with (for instance) chicken, soft cheese and salad, you have a whole meal in one giant sandwich.
Otherwise, flasks of tea and/or coffee, wine, beer and/or fruit juice, some nice fruit for afters and a bar of chocolate – and you have a complete picnic.