Asked at the shelf, answered the same way.

On nearly every fare in the table, yes — the under-seat box travels with the ticket. What changes is its size. The leanest fares on Jetstar and Scoot, for example, bring only that box and nothing for the locker.

Practically never. Locker boxes start around 46 cm on the longest side, while under-seat boxes stop at 45. A bag built for the locker is wider and taller than the space beneath the seat in front.

Because most airlines publish two allowances: one for the piece under the seat and one for the piece in the locker. They are separate boxes with separate weights, and a fare usually buys both or only the first.

The gate decides. Carriers with a published sizer can charge a fee equal to a checked bag, and some will move the bag to the hold. Two centimetres over is still over, which is why the stamps here are strict rather than generous.

Yes. Published cabin weights count the packed bag, not the contents. That is why a scale sits in the cabin kit — the difference between 6.9 and 7.2 kg is the difference between boarding and paying.

No. It lives in the browser it was built in, which means a list started on a phone stays on that phone unless the items are added again elsewhere.

Amazon shows the current price at checkout and that figure wins. Cards on this site are orientation, not quotes, and the gap can be a few dollars either way.

Of course. The ASIN is the same identifier Amazon uses, so a product name pasted into the Amazon search bar will find the listing without any link from this site.