Start with your seat-side items
Make a small pile containing your documents, phone, headphones, any necessary medication, a warm layer and the book or tablet you expect to use. Add your charger and whatever else genuinely needs to stay with you. This exercise often produces a smaller requirement than starting with a large tote and filling all its pockets.
Separate things you will reach for repeatedly from things you merely want close by. A zipped inner compartment can keep documents from slipping out when you remove a sweater. Snacks and a water bottle, where permitted, should be accessible without exposing electronics. Avoid a bag so tightly filled that every retrieval becomes a complete unpacking exercise.
A soft bag still has dimensions
Check the operating airline's personal-item limits and measure the bag when loaded. Soft sides only compress if the contents can move. A rigid laptop, a full bottle or a hard camera insert can prevent an apparently flexible tote from fitting a smaller space. Do not rely on a retailer's statement that a bag is suitable for all airlines.
Seat structures differ, and under-seat space may contain equipment or supports. Follow the crew's stowage instructions and do not assume every seat offers the same usable area. If keeping legroom is important, a modestly sized bag with fewer hard objects can be more comfortable than using every permitted inch.
Carry the two bags together
Test the personal item with the suitcase or backpack you already own. A sleeve that slides over a suitcase handle is useful only if it fits securely and the load does not tip the case. With a backpack, a small shoulder bag may be easier to manage than another pair of shoulder straps.
Walk through a doorway, turn around and put both bags down as if you were boarding a train. Check that you can hold a rail or present a ticket without balancing everything on one arm. A top zipper and a comfortable handle are often more useful than several decorative pockets. Keep the setup manageable enough to carry unaided when a lift is unavailable.
