A towel is about the most massively useful thing an interstellar hitchhiker can have.

Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.

But what about the End of the Universe? We'll miss the big moment."
I've seen it. It's rubbish," said Zaphod,"nothing but a gnab gib."
A what?"
Opposite of a big bang. Come on, let's get zappy.

If you try and take a cat apart to see how it works, the first thing you have on your hands is a non-working cat.

So this is it," said Arthur, "We are going to die."
"Yes," said Ford, "except... no! Wait a minute!" He suddenly lunged across the chamber at something behind Arthur's line of vision. "What's this switch?" he cried.
"What? Where?" cried Arthur, twisting round.
"No, I was only fooling," said Ford, "we are going to die after all.

An international power supply is the device which means it doesn't matter what country you're in, or even if you know what country you're in (more of a problem than you might suspect) - you just plug your Mac in and it figures it out for itself. We call this principle Plug and Play. Or at least, Microsoft calls it that because it hasn't got it yet. In the Mac world we've had it for so long we didn't even think of giving it a name.