Nothing here yet.
The mistake is packing for the holiday you wish you were having rather than the one you've actually booked. People buy a stiff linen set for a city break with a lot of walking, or three evening dresses for a trip that's mostly beach and chips, and end up wearing the same two things on rotation while the rest sits in the case getting creased for nothing.
The pieces that actually get worn are the ones that talk to things you already own rather than arriving as a whole new outfit with nowhere to go. A plain linen shirt over a swimsuit works at lunch and then layers under a jumper when the evening turns, a simple cotton dress does the same job in a different shape, and sandals that aren't brand new on day one save you from blisters on the only cobbled street in town. Think about what you're doing more than what you're wearing: a sun dress and flat sandals for wandering and markets, something with a bit more shape and a pair of espadrilles for dinner, a cover up that can go straight from pool to table without a change of clothes in between. Early and late summer call for one more layer than you think, a light cardigan or shirt that takes up almost no room but means you're not shivering on a terrace at nine in the evening. High summer in proper heat wants natural fabrics that breathe, because anything synthetic will have you peeling it off your back by mid afternoon.
Before you buy, check what the fabric actually is rather than how it looks on the hanger, since a cotton blend with too much polyester in it will crease differently to proper linen and cling in a way that's uncomfortable once you've been sweating in a queue for twenty minutes. Look at lining, too, particularly on anything pale or sheer, because a dress that's fine indoors can turn see through the second you step outside into real sun. For fit, go by how something sits when you're sitting down and standing up, not just standing in front of a mirror, since holiday days involve a lot of both, and anything with a fitted waist is worth trying with a slightly fuller stomach than you're expecting to have after lunch. Watch necklines and straps for sunburn lines you'll regret later, and check that sandals have a sole with a bit of grip, because wet stone steps and flat leather soles are a bad combination you only discover once.
Reach for this sort of thing from the week you book the trip, not the night before you pack.
Nothing here yet.