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: 
A cabin crew member here...

In general, flight attendants will be happy to give you the extra meal after the service is done, because they know it will be [thrown after landing](https://travel.stackexchange.com/questions/19850/do-airlines-recycle-uneaten-unopened-pre-packaged-food/19852#19852) anyway. Out of experience, there are always some extra meals, at least one or two. Sometimes passengers simply do not take a meal, some other times there's just an extra meal or two loaded for whatever reason. In some other flights, there's a shortage actually. They usually cover for this by using the crew meals, and this is rare anyway.

Is it ok?
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Yes, nothing wrong with it, flight attendants will not think badly of you. As long as you ask nicely, of course. One more thing, all the meals usually get heated at the same time. Once heated they are good to be eaten for a certain time, then they can't be served to passengers. So, if you feel you want an extra meal, ask for it. I have seen so much food being wasted while I was sure many people were hungry but were shy just like you.

When to ask
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When they are serving you, give them a hint that you would love to have an extra meal if it's possible after they are done. Personally, when this happens I might give them right away if I know that there are extra meals. Otherwise, I will just wait until service is done and then come back with the extra meal, or apologize if I couldn't find any.

Note: I am talking about full-service airlines. For budget airlines where food is bought onboard, you can pay extra and get more food. That's a different story.
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...