Learn English – What does the phrase “held in confidence” mean

Jamming into one's throat means to make absolutely sure the person hears you and cooperates with whatever you're jamming into his throat.

So the captain, Pat Rafter, is saying that he'll make absolutely sure his team gets the message that they can't afford to be complacent when playing against the Chinese. They've got to be tough, or they won't win.

And the point made in the other example is that most vegan/vegetarians don't force their views on everyone else, or even look down on others, as some people seem to think.

If you're planning to use this expression, consider a more common form: "shove down one's throat". This NGram illustrates that "shove down his throat", though rare, exists; whereas "jam into his throat" does not even appear. (The same goes for "their throats", and, I assume, all other forms.)

"off the top" in general and here means the first 5 hours

In "off the top of my head" it means the first idea that came into my mind. Similar principle