Question: I am just curious if last minute hotel deals is actually a thing. I am not a big traveler and have no clue.

But in theory if a hotel has a bunch of empty rooms for the current day, it would make sense to rent them at a reduced rate as opposed to letting them be empty.

Is this actually a thing that could be leveraged?

I am going on a road trip, and the last leg of the trip could take many variations on a moments notice and was wondering if this is something I could take advantage of.

Answer: 
**Yes you can ask.** And **I have successfully asked for extra food in the past** (i.e. over the last five years and as recent as a month ago). One time when asking for a second sandwich I was even proactively offered a third one later on. I also typically ask for two beverages and never had that refused. 

Of course they have no obligation to give you extra food but on a full service airline they are usually happy to. (Since you mention a first meal I assume you are on a full service airline. If you had to pay for your first meal, you'll have to pay for the second as well.)

A good strategy is to **ask when they have just finished distributing meals and you have already finished yours** or if you already know to be hungry, you could tell them **when you get the meal that you would be interested in a second serving.**  

Be nice, don't interrupt and you have good chances.
After seeing the comments here, I tried it myself.

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Can you get it? - Yes you can, still today.
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I asked in China Eastern and Korean Air, both in economy and large cabin, in 2016.

You can ask an attendant once you finish eating, and he/she kindly starts to check if they can serve it for you.

However, whether it is only a main dish or whole dish depends on the airline (and attendant oneself and also random chance). In China Eastern I only got a main dish, but I didn't like to bother to complaining about it (and it was enough), so didn't make any further actions.

When you ask, the tips by other answers would likely work to your favor; be polite, wait for the end of the distribution of meal, and don't disturb. However, I want to add one more tips; you shouldn't ask it shortly before the start of collections of finished meal. In this case, attendants have to care about *only you* once after they finish collecting all the other passangers' meal. So make sure your second meal is going to be collected with others'.

However, some airlines don't allow it for whatever reasons. I asked at Asiana Airlines a few times (different flight, route, and crew) but I got declined in all of them. In fact when I asked one attendant she immediately got to ask a more elderly attendant (maybe a chief) and the answer was NO. So in these airlines, you could never get an extra meal, unfortunately...