The spare-of-everything instinct, and where it is right

What follows is the working version of carrying spares: the decisions in the order you actually meet them, with the reasoning attached.

The test is replaceability, not importance

The question is not how much an item matters but how long you would be stuck without it and how hard it is to obtain locally. Socks matter and are replaceable in twenty minutes almost anywhere, so a spare pair is convenience rather than insurance. A prescription lens, a passport or a charger for a proprietary connector can stop a trip for days, which is a completely different category.

Sorting your packing list by that single question removes most of the duplication people carry by reflex.

The short list that earns its weight

Glasses or contact lenses, if you cannot function without them, because an optician abroad needs a prescription and time. Prescription medication in more than the exact quantity, because delays happen and refills abroad range from awkward to impossible. A second payment card on a different network, stored somewhere other than your wallet, because card failure abroad is common and immediately disabling.

At the airport, a charging cable and adapter, because the failure is cheap to prevent and awkward to fix at midnight.

Documents are redundancy of a different kind

A photograph of your passport data page, stored where you can reach it without your phone, materially speeds up replacement at a consulate. Booking references, insurance policy numbers and an emergency assistance line are worth holding offline, since the moment you need them is often the moment you have no data. A printed copy weighs nothing and survives a dead battery, which is the specific scenario the digital copy fails.

In practice, storing one copy in the bag and one on your person covers theft of either.

Where redundancy is a trap

Spare clothing is the most commonly over-carried category, because clothes are available everywhere and washable overnight. A second pair of shoes beyond one spare is almost always dead weight given the volume they occupy. Backup electronics — a second camera body, a spare tablet — are heavy insurance against an unlikely failure with a cheap workaround.

Each spare has a fixed cost in weight and volume paid on every day of the trip against a low probability of use.

Redundancy in systems, not objects

Two ways to reach money, two ways to prove identity and two ways to reach the internet cover most travel failures without duplicating hardware. An eSIM alongside a physical SIM is redundancy that weighs nothing, though device support and country coverage vary. Splitting cash and cards between the bag and your person means one theft does not clear you out.

This is generally a better use of thought than carrying two of any physical object.

Border and customs rules are national and are the ones worth double-checking.

Buy locally on purpose

Deliberately planning to buy sunscreen, insect repellent or a towel at the destination removes bulky, heavy and liquid items from the bag. It is also usually cheaper and better suited to local conditions, since products are formulated for the climate they are sold in. The exception is anywhere genuinely remote, where the first shop may be a day away.

Check whether you are going somewhere with shops before deciding you must carry everything.

The takeaway

Duplicate only what stops the trip and cannot be replaced by lunchtime. Everything else is shopping.

The trip goes better when the bag is boring.