Your main travel backpack is full of clothes, but tomorrow you only need a bottle, a layer and a few essentials. A packable daypack can solve that mismatch. Whether it is worth bringing depends on where the main bag stays and how much support the smaller bag needs to provide.
Give the second bag a day to cover
Write down what you expect to carry during a typical outing from your accommodation. A small sightseeing load is different from a full day with camera equipment or a laptop. The first may suit a light foldable bag; the second may call for more structure and protection.
Also decide where the main backpack will stay. A daypack is useful when your accommodation provides a suitable place for the travel load. On a moving day when you must carry everything, it can become another piece to manage rather than a reduction in baggage.
Folded size is only half the comparison
A compact packed pouch looks appealing, but examine the unfolded straps, opening and back panel. Minimal padding can be acceptable for light contents while allowing a hard object to press uncomfortably against you. The smallest folded bag is not automatically the most useful day bag.
Check whether the design includes a suitable bottle pocket, secure closures and a place for small essentials. Avoid assuming a lightweight bag protects a computer simply because the computer fits inside. If you need a laptop sleeve or added case, count that extra weight and volume in the comparison.
Some structured daypacks can travel flat inside a larger pack even though they do not fold into a small pouch. Try that arrangement before buying a foldable replacement. It may be a better fit for your everyday load, provided the combined packing space works.
Account for the extra layer of baggage
The daypack adds its own mass and occupies space on every travel leg. If you intend to use it only once, consider whether your main backpack can be partly emptied for that outing or whether a bag you already own serves the purpose.
If you plan to use the second bag as a separate item on a flight, check the carrier's allowance for the ticket. A bag that was inside the main pack does not retain that status once you carry it separately. Keep the return journey in mind if souvenirs make you want to use both bags at once.
Practice the morning handoff
At home, transfer the outing essentials from the travel backpack into the proposed daypack. Notice which items are easy to forget: keys, medication, a charger or a particular document. A small reusable essentials pouch can simplify the transfer, but it should not be so large that it dictates the entire daypack choice.
Load the daypack as you would use it and walk around. Check that the straps adjust sufficiently and the contents do not swing or jab through the fabric. If it carries the normal day load comfortably and stows without disrupting the main bag, it has a clear role. If it needs several protective inserts and extra organizers, a more structured small pack may be the cleaner solution.
