The Hamptons sit twenty minutes from Montauk and run on a completely different dress code, which is why packing one bag for both goes wrong. East Hampton and Sag Harbor want polish rather than effort: cream, beige and white, with navy used sparingly and one piece of real jewelry doing the work. Early September stays warm through lunch and turns breezy on the water, so the layer you bring matters more than any jacket. The day is a club lunch or a pool, the evening is dinner in the village, and the walk between them is uneven sidewalk and, if you are lucky, a dock. That rules out a narrow heel and makes a flat sandal the most useful thing you own. What follows is an eight piece day look, a four piece evening look, and nothing that needs more than expedited shipping to arrive in time. The other thing worth saying plainly is that the Hamptons reward restraint. One good bag, one good sandal and one piece of jewelry beat a suitcase of options, and the weekend is short enough that repetition is invisible. Order by Friday morning and take expedited, because standard will not make it.

The structure is a printed silk blend maxi over a square neck one piece, with a small leather tote and a flat thong sandal. It reads finished without looking like you tried, and it holds up at a club, which is the actual test. Seersucker and silk blends are the right fabric call here because they move in the wind instead of sticking, and they come out of a bag without pressing. Keep the bag small. Village dressing punishes a big tote, and you need a phone, a cardholder and a lipstick between lunch and dinner. Then add the three quiet pieces that carry the whole weekend: a cotton sarong for the pool, a cream gauze cover-up you can pull straight over a wet suit, and a ribbed cashmere cardigan for the boat at six. On fit, halter maxi styles run long, so check the length against a flat sandal rather than a heel before you commit. One more point on colour. The palette that works here is cream, beige and white with the navy used sparingly, because beige photographs richer than white and hides a day spent in a car. Buy the plainest version of every piece.

We would not buy a new evening dress for this weekend. A plain black midi you already own, with a good bag and one strong pair of sunglasses, will look more correct in Sag Harbor than anything bought in a hurry. Put the money into the flat sandal and the cardigan instead, because those are the two things you will use every day and again next summer. The sarong is the piece people skip and then wish they had, and at this price it is not a real decision. What we would avoid is matching the whole look to the palette. All navy and white with a navy and white bag reads as a costume rather than a wardrobe, and one wrong note is what makes it look like yours. If you take one thing away, pack the cashmere cardigan. Everyone underestimates the water at nine o'clock in September. We would also resist buying a second pair of evening shoes. Two dinners do not need two sandals, and the pair you already trust will get worn either way.