Airline lost my baggage?

So on the 16th of December I was on an outbound flight from Chicago to Kuwait with a transit in Jordan flying royal Jordanian. When I arrived at the baggage claim area my bag had not arrived and so I filled out the paperwork and got a reference number and all before I cleared security.
It's been 5 days and most sources online say if it hasn't been found within the 5 days it will unlikely be found within 21 days and so now I have the issue of trying to remember what was in my bag and its value at which I bought it at and the provision of receipts especially for things I got as gifts for which I never received the receipt for. I have a pair of diesel jeans I got as a gift for example that were about $300 but I feel like the airline would never believe me without a receipt.
Also going along the lines of being broke and not being able to afford my own $300 jeans I'm a college student and my next semester of classes will start by the time the 3 weeks are over and the airport that I fly back to (Chicago) is really far from my campus so is the compensation form from the airline something I can fill out online?
Sorry for the long question I'm really worried I just lost all of my favorite clothes and I have no idea what to do about it.

Can I put a empty backpack inside a duffle bag when flying?

I'm flying to LA soon and I want to take both a duffle and backpack, I don't want to put my backpack inside my suitcase as it's expensive and I don't want to lose it, I won't be using the back pack at all it'll be staying in the duffle but will the airline think I'm trying to get extra luggage?