Once upon a time, there were no picnics.  People ate outside all the time but that was only because there was no inside to eat in.  The discovery of fire turned every meal into a barbecue, but still there were no picnics.  Only after the invention of dining rooms (or at least kitchens with eating areas) did picnics make their debut.

A meal is a picnic only where there is no good reason to eat outside.  If, for example, you are stranded alongside the highway and decide to eat a granola bar to keep from fainting while you wait for the tow truck, you can’t call it a picnic since you are not there by choice.  Put simply, a picnic is a meal eaten outdoors by an otherwise intelligent and responsible person who had the option of eating indoors but chose, against all reason, not to do so.

Of course, you won’t find that sort of elucidation in the dictionary.  Mine (The American Heritage Dictionary of the English Language, since you asked) limits its definition to “a meal eaten outdoors on an excursion,” which really doesn’t tell the whole story.  The second meaning, “an easy task or pleasant experience,” not only doesn’t tell you very much but makes absolutely no sense since picnics are neither easy nor pleasant.

Take, for example, the problem of chairs.  Generally speaking there are no chairs at a picnic.  At best, there are backless benches that threaten you with splinters in inconvenient places.

The only way to have a proper chair at a picnic is to carry one along, which seems silly when there are plenty of chairs sitting at home in your dining room where you could have eaten if you wanted to.  Besides, you already have your hands full with a cooler of beer, a bucket of chicken and a bowl of potato salad which you are in danger of dropping in the parking lot.  With all that, how in the world do you think you are going to carry a chair, too?

The main reason you need a chair on a picnic is because if you don’t have one, you have to sit on the ground which, of course, is dirty.  Lacking a chair, you’ll need to bring a blanket along to spread on the ground, just one more thing to carry with the beer, the chicken and the potato salad.  You might as well bring a chair.

While you are carrying the beer, the chicken and the potato salad from the car and looking for a place to set up your chair or spread your blanket, the beer and the potato salad are getting warm while the chicken is getting cold.  By the time you are sufficiently arranged to eat, the temperatures of all the elements of your meal will have met at a uniform lukewarm.

Uninvited guests of the phylum Arthropoda, order Insecta, are as plentiful at a picnic as chairs are scarce.  Most typical are flies which are partial to cold chicken, bees who are fond of warm beer and ants who are attracted to potato salad at any temperature.  Now, perhaps you have flies, bees and ants in your dining room.  If you have, I suppose you might as well eat outdoors, provided you can solve the chair problem.  But if you haven’t, you should seriously question your motives for this whole venture before you drop the potato salad in the parking lot.

If, indeed, you really like warm beer, wouldn’t it be much simpler just to take a trip to England?
  

From The Nonexistence of Rutabagas and Other Marginal Considerations
Erinear Books