Interim purchases, the bag-fee refund, and the deadlines that start the day your bag finally arrives.
A delayed bag is a claim in its own right, even if it turns up. The airline owes you the reasonable things you had to buy because the bag was not there: clothes, toiletries, a phone charger, medication, whatever you needed to get through the days without it.
Keep every receipt. “Reasonable” means what a sensible person would buy in your situation, not a new wardrobe; but airlines may not cap it at a flat daily amount or pay half for clothing on the theory that you keep the clothes. The US DOT has fined airlines for both.
The bag fee comes back too. Under the DOT’s 2024 refund rule the airline must refund the checked-bag fee when a bag is delayed more than 12 hours on a domestic flight, 15 hours on an international flight of up to 12 hours, or 30 hours on a longer international flight. You have to ask; the letter this site builds asks.
Deadlines. On an international trip the written claim for a delayed bag must reach the airline within 21 days of the day the bag was delivered to you. That clock does not start until you have the bag, so a bag that is still missing has no deadline running yet, but do not wait for it: file the interim-expense claim as soon as you have receipts and add to it later.
Work out your own claim → Free. Takes about ten minutes.
No. The purchases were made because of the airline’s failure; they are your loss to claim, not a loan.
Yes: the interim purchases, and the bag fee if the delay passed the threshold for your flight.