Sunscreen? Check. Flip-flops? Check. Trashy novel? Check. Hostess gift? Er . . .

The summer exodus begins this weekend, with thousands of city folk invited to weekend in the country, hang out at the beach, overeat, overdrink and oversleep in someone else's home. It's a lovely custom, especially for the invitees who would otherwise spend weekends at home, feeling sorry for themselves.

If you're one of the guests, consider yourself lucky. That means you've got at least one pal who a) owns a weekend place and b) can tolerate you for more than three hours. And that, dear friends, is nothing to sneeze at.

Being a good houseguest can be tricky. It implies a certain level of intimacy, in the platonic sense of the term. It means pitching in without getting underfoot. It means not being embarrassed to see everyone in bathrobes (or less.) It requires tact, flexibility and generosity -- which is tough enough when you're sober, much less on your third gin and tonic.

But before you jump in the car, take a moment to consider a hostess gift -- which sounds prissy and old-fashioned because no one has come up with a better name for it. It's traditionally a symbol of friendship, and good manners say you don't show up empty-handed. As a public service to guests and hosts everywhere, we offer a short primer on what to bring, what not to bring and what will ensure you'll be invited back.

Lesson No. 1: It's a three-day party.

"Eat it, drink it, or burn it."

That's the gift mantra of Roman Terleckyj, veep of artistic planning at the Kennedy Center and owner of a country house in St. Michael's.

Think about it; it's more than just a weekend visit. Your friends are hosting a 72-hour party for their nearest, dearest and those with potential. Now calculate what it will cost for them to entertain everyone, and you start to get the picture.

"The best thing a person can do is drag in a case of wine," he says. "It doesn't have to be expensive wine. When you have a lot of people out for the weekend, it's amazing how much wine you can go through."

Consider: Overnight guests aren't driving. Lazy brunches slide into cocktail hours and then into dinners. Terleckyj usually has four to five summer houseguests and an additional 10 neighbors in for informal meals. There's lots of munching, lots of people in the kitchen, lots of laughter.

The gourmet goodies that might be the perfect gift for a dinner party don't work as well in casual settings. Terleckyj favors quantity over quality: The fixings for a bunch of margaritas instead of one bottle of expensive champagne, pies and baked goods instead of gourmet chocolates. "Wasted in the country," he says.

Best bets: Food that is easy to serve. Liquor, wine and beer, of course. Jams, chutneys, sauces. Cocktail hour nibbles like hard cheese, crackers, canned pates, nuts, mustards, those funny little pickles.

Nothing big, unless you clear it with the host in advance. "Someone brought me venison, and it's taking up most of my freezer," says Terleckyj. "I'm still waiting for her to come back and cook it."

Whatever you bring: Remember, this is a gift, which means the host can serve it to guests or save it until everyone goes home.

Lesson No. 2: Spoil your host.

Some hosts like bulk; other like bijoux.

"I think it ought to be a luxury item -- not expensive, but something I wouldn't buy myself," says Baba Groom, president of a trading company and owner of a 50-acre farm on Maryland's Eastern Shore. "I wouldn't buy the best olive oil or the best vinegars for myself, but I love to get them."

Groom has a devoted following of houseguests who have lavished goodies in hopes of return invitations. Her favorites: perfumed candles (really nice ones), good hand towels and cloth napkins (she doesn't use paper ones) or lovely soaps. "And of course, eternally, nobody objects to a $20 bottle of wine, which is just wonderful." Then there's the pair of rubber gloves with black lace trim? She adores them. Go figure.

One friend and repeat guest always takes care of breakfast, bringing lox, bagels, eggs, bacon, coffee and then preparing the meal. "When you pitch in with the hostess, you're taking a lot of pressure off her," says Groom.

The only gift she warns against is cut flowers -- a classic hostess gift, but best saved for the city. Most weekend houses have gardens or plenty of plants, and a beautiful bouquet has less impact.

Lesson No. 3: You aren't the decorator.

Generally speaking, nobody needs more stuff.

The June issue of House & Garden magazine has suggestions for weekend hostess gifts, most of which we believe are very swell and very silly. The editors think a Christian Lacroix Praline teacup and saucer ($290), Vera Wang decanter ($125), Etruscan pewter carafe ($295), or crystal rose bowl ($250) would be nice. Maybe if your host is, say, Prince Charles -- but we still think he'd rather have a good gardening book.

No matter how rich you are, or how rich your host is, it's better to give an expensive comestible than an expensive tchotchke. If you want to spend $290, a case of good wine is a better bet than the teacup.

"Don't think of it as your job to decorate someone else's house -- that's where you get in trouble," says the owner of a new beach house in Rehoboth. The owner (a lobbyist who asked not to be named lest everyone he knows hits him up for invitations) and his wife have hosted a number of friends at the house. "Almost everyone has asked what to bring," he says. "We try to be as specific as possible because we're worried people will show up with Hummel figurines."

One good friend, angling for lifetime visiting privileges, sprung for a monster gas grill -- which qualifies more as a housewarming present than hostess gift and was enthusiastically received. (A good choice for hosts with grills: steaks, ribs, cool barbecue sauces that can be used over the weekend or tossed in the freezer.)

If you must bring a gifty-gift, says the lobbyist, "make it small. A tiny unwanted thing is much better than a gigantic unwanted thing."

Small and wanted: books, videos, DVDs. Into every weekend a little rain must fall, not to mention lazy afternoons in the hammock. "I always give books, fiction mostly," says Willee Lewis, president of PEN/Faulkner. Her hostess gift this year: collections of short stories by John Updike and E.L. Doctorow.

Books work for hosts and guests alike; short stories especially are well-suited for catch-as-catch-can weekend itineraries, but a meaty mystery novel is always fun. Recently released movies or classic films work well for summer houses, along with a gift basket of microwave popcorn, Milk Duds, Junior Mints and other concession stand goodies.

Lesson No. 4: Cheapskates don't get invited back.

Stop at the ATM on the way.

It goes without saying (but we'll say it anyway) that good houseguests offer to pay whenever cash is required. If you and your hosts go out to the movies, you pay. Swing into the gas station, you pay. Ditto for ice cream cones, beach drinks, et al. If the visit is long enough, you should offer to pay for dinner at a restaurant.

If you didn't bring something upon arrival, it is perfectly fine to send a small gift after the weekend, assuming you have carefully surveyed the house and select something charming/useful/fun that matches its style and hosts. (Uncertain? Send wine.)

Final Note: A hostess gift is not a substitute for a thank-you: It's good form to send (not fax, not phone, not e-mail) a handwritten note expressing sincere appreciation for hospitality.

We assume, of course, that you've been a gracious and delightful guest and your host can't wait to invite you back. If you were a boor and a bore, the thank-you is even more important, trusting you sincerely apologize for drinking too many margaritas and jumping naked in the pool -- unless everyone else did, too.

Let the games begin.