Checked-in luggage, Last in First out, is it true?

It's not really true - especially if you have a transfer. The idea behind this concept is of course that if your bag is last, it'll go near the cargo-hold door, and come out before anyone elses. The reality is that the luggage handlers put your bags on their carts in an arbitrary place and hook them up in an arbitrary position of their little luggage-cart trains. Then, they arbitrarily load them onto the plane. The net effect is that everyone's luggage is scrambled - even more so after the people at the receiving airport unload it, and compounded further if you have connections.

At Heathrow Airport (LHR), bags are individually loaded into containers. The carts move at high speed to the aircraft.

However, as the carts are like trains, where they meet some have to wait. However, late bags go in last, but can come out from either side. So I would say the process is random. You can take a look at this video

It depends a lot on the circumstances and the airports involved. But yes, that can very well be the case.

So, whenever I had a short transit (< 30 mins), I received the luggage among the first at my final destination. The hypothesis being of course that since my luggage arrived way after the others, First-In-Last-Out implies that it gets out first.

I can only offer personal observations, but I noticed this quite often - very late luggage (being Business class also helps) gets luggage first. Note that this does not imply that always, later luggage comes out earlier: At most airports, the big bulk of luggage gets collected together and stored in the airport with one or two charges. These come in together, no matter the order.

I have seen on some airlines (mainly Emirates, but I think one more has it but the name escapes me) tag your bags with priority clearance if you are flying business or first.

However, it is not guaranteed to be the absolute first bag unloaded - you are just guaranteed it won't be dead last; and even then only at the airline's hub.

Bag load configuration depends heavily on the aircraft. Some larger aircraft carry standard size cargo bins which are loaded at random, and then distributed based on the current configuration of the aircraft (the exact load order is determined by the load master).

Upon arrival, one (or multiple) doors are opened and luggage is unloaded; typically from one side of the aircraft - it is almost always the opposite side from where passengers are disembarking.

If your flight is transit; then you might see two doors open where one is for loading and the other unloading luggage.

Luggage then makes it to the luggage loading bay, where it is put on a conveyor belt; and depending on the airport you might have multiple miles between the loading bay and the final deposit chute where luggage arrives.

During this travel time for luggage, it may be subject to multiple scans, stops, re-routes based on the particular airport - or, as is the case with some airports, it might just be some bloke chucking your bag through a hole onto a belt, which then meanders down to you (I'm looking at you, ISB).

Anyway, all that means is that there is no rhyme or reason for the order in which bags start arriving at the collection turnstile.

Some things that do make a difference:

1. Luggage checked "gate side" (usually, baby strollers and the carry-ons on full flights) are unloaded separately from the normal luggage, and this means they usually arrive quicker.

2. Soft bags (as others have mentioned) may be offloaded quicker - but this depends entirely on how they were loaded in the first place.

3. Odd-sized luggage or over-sized luggage is usually handled separately.