The bag is the one item we carry every day and the one we never try on: the four requirements that are not negotiable

There is one detail in this story worth more than the entire guide: a 28-year-old woman was more afraid of back pain on a Tuesday than of a hangover on a Saturday. That is not a joke about ageing. It is the bill paid by anyone who carries a bag every day that was not built to be carried every day.

The fashion editors who put this list together started from an admission: we almost never try the bag on. We try jeans and dresses fifteen times over, and we buy the bag because it looks good on a hook - then spend months discovering what does not fit in it and how short the strap is. That is not a triviality. An awkward bag ruins every subsequent commitment in the day.

Size and internal pockets

The first requirement is not aesthetic. One editor says she spent years carrying a small, fashionable bag plus a second canvas tote crammed with a laptop and a planner, until she admitted she needed one large, universal shoulder bag. Another is even more specific: the bag must hold a computer, a planner, gym clothes for after work, a toiletry bag and a lunch box.

Not everyone agrees. One of them deliberately chooses a medium cross-body model: "I prefer a moderate size that fits lunch, my e-reader and makeup. With bigger bags I fill them with useless things." This is an honest cut - size is not a virtue in itself, it is a decision about how much you are prepared to carry.

What they all agree on is compartments. Keys must be kept away from the phone so they do not scratch it, and at least one zipped internal pocket for valuables is mandatory. Not because of theft - because of the time lost searching.

Zip or clasp

The second biggest complaint is an open bag. A closure at the top - zip or clasp - is not up for negotiation. It protects your things on public transport, in rain, wind and strong sun. Opinions split again here: one editor likes a model with a single automatic clasp that opens instantly, another says that without a zip she loses things because she is untidy. A third has both.

Material and colour

Leather or nylon - the material has to survive everyday use. The colour should be dark, so every scuff and mark from dark jeans does not show. One of them has a burgundy bag and says it goes with everything, in winter and summer alike. That is entirely practical logic, not fashion.

Elena Peña, founder of the Spanish brand MICUIR, reduced the whole discussion to a list: moderately large, with a firm base that holds its shape, with comfortable handles or a long shoulder strap, with an organised interior, with a secure closure, with an aesthetic that survives both the office and a night out, and made of quality material.

What these recommendations lack is the price - and here it is worth being direct. The models the editors list range from around 135 euros for a classic foldable nylon to 650 euros for a large leather bag. That is a range in which the difference is not only the leather. But the list of requirements itself does not demand expensive: a firm base, a dark colour, a zip and one internal pocket are not luxury, they are construction. The question is how many fashion brands actually do those four things, and how many are selling shape alone.