This is one of the few christian traditions that I think has merit. A measure of gratitude for the fact that you've decent food, regardless of where you bestow that gratitude, helps keep the world in perspective.

No, it is a reflexive / conditioned means of giving thanks to god for his general provision including the things like the health and skill of the family's "bread-winner(s)". It is also a way to condition people not to directly (if at all) credit themselves or any other human with obtaining food or finances, lest god not get "all the glory".

In the Christian system, god gets 100% of credit for all positive outcomes, humans ultimately (sometimes indirectly via Satan) get all the credit for negative outcomes. So the mealtime prayer is a ritual for cementing that.

God has a great gig.

I had fallen out of the habit of "saying grace" and made the mistake of digging into a restaurant meal before doing so in the presence of my elderly father. He found that quite disgusting. I apologized and let him say grace. I don't mind accommodating believer's tender sensibilities and totemic beliefs when I remember to, but I have to say, it's just as well my parents had me late in life and I, in turn, became an unbeliever late in life, it spared us both a lot of hassle.

Ha ha! It took such a long time for me to get used to eating a meal without feeling like I was forgetting something.

God takes a lot of credit for random luck.

Here's how life really works:
You plant your crops. They either grow or they don't, depending on the weather amongst other factors. You hunt the wild boar. You either spear it or you don't, depending on your skill and, to a degree, just random chance.

Religious people like to think they can skew the odds in their favour through prayer. God will make sure that the crops grow. God will let the hunter bring back their prey. So better say 'thanks' to him, otherwise he might not bother next time round.

The hunting scenario is largely redundant. The crop growing one isn't. Floods, droughts and both plant and animal disease outbreaks all happen, and can all result in shortages of food and water. Especially in less developed parts of the world.

Of course when you get all of your food from the supermarket, it becomes more of a superstitious ritual than anything. But the root stems from the human need to feel it has some degree of influence over things that it can't control.

to let the meal get cooler?

To give thanks to a "God" that had nothing to do with putting the food on the table.
Never mind the farmers who grow the crops or raise the livestock. (God did it, not them)
Never mind Mommy and/or Daddy's employment that put money in their pockets. (Pffft, that was God)
Never mind the business that sells said produce to Mommy and Daddy. (God sells that shit like a dope pusher)
Never mind Mommy and/or Daddy taking the time to prepare a hot meal for their family. (That was God. All God)

Maybe it's to pray because their thankful to be alive. Never mind modernl science has drastically increased the average life expectancy of humans over the past century or so. (Fuck them, it was all God)

Sorry everyone if my reply(s) sound aggressive.
I've had a pretty shitty week.