I am fascinated by information that is also a thing. In this day and age, we have no real problem viewing information as something pretty abstract. It can be easily copied, moved, passed around and even altered with only trivial effort. This is, by an large, a pretty cool thing, but I like thinking about the exceptions to it (or in some cases, the variations), both for what it suggests and (because I'm a shameless nerd) how it creates hooks.
Ok, so what do I mean by this? The easiest way to think of it is historically. Flash back to sometime before the printing press - if you have a book that details some complicated procedure, that physical book is, for all intents and purposes, the book _is_ the information. Copying it is a serious effort, so the main way to procure the information is to steal the physical book. That makes it an excellent macguffin, and it also suggests that the person who could copy or transfer the data (through, say, photographic memory, or some manner of duplication spell) would have a distinct advantage.
However, what some of you are noticing is that, even in this extreme case, the information is not _really_ the same as the object. The information is still abstract, and you can still _do_ all the same things (copy, transmit, etc.) it just is harder. And that's completely true, but it's important to note that "harder" is not necessarily a trivial obstacle. It is, in fact, understanding these obstacles that makes the questions surrounding information as a hook.
As an ilustration of this, consider codes. They are a classic element of much adventure fiction, and the simple reality is that while codebreaking is a fun exercise for a certain kind of mind, it's not really much fun in game. But practically speaking, a code is just some incomplete information: having the coded note doesn't help you, but having the coded note and the cipher key is something complete. As such, if you have one, then you have an almost automatic hook for the other, and that's where things can get wacky. It is entirely possible that both ends (the note and the key) are simple information (as in the case of a letter substitution cipher) but assuming that secrets actually need to be kept, things are often a little more complicated than that.
One common trick is to embed the key in a physical object (see how we come back to the premise?). For example, you can put a message on a strip of paper so that it only lines up when it's wrapped around a cylinder of the right size. This is not a great precaution - if the other side knows about it they can just keep trying different size cylinders until they get a match, but if they don't know to do that, it can be a daunting barrier - but it illustrates something. There are actually _three_ things at work here: the message, the key (the cylinder) and the knowledge of how to use the key.
Suddenly, we have three hooks, all without the necessity of some sort of convoluted "You need the sword to kill the dragon, you need the scroll to get the sword" epic fantasy kind of chain. All by itself, that's a win.
There are about a zillion books on the history of ciphers, and any one of them will provide a font of ideas for play. heck, just poke around Wikipedia - start with the Playfair Cipher and just start following links. The big thing you'll find is that most of the cleverest methods aren't technology dependent, which means they're just as useful for your D&D game as they might be for your Leverage game.
1 - Systems like this are actually surprisingly common and are sometimes referred to as "Security through obscurity". If you have all the necessary information, they're trivial to crack, but there may be some barrier to finding the information, especially if it's a needle in a haystack. Consider bible codes: If I send someone a message that is entirely composed of "Page:Line:word" references, that's very easy to crack _if_ you know what book I used and you can get a copy of it. If you don't, then it may well be impossible (even in very modern contexts). This is a great way to make an old book a great adventure hook without making it magical in the least.
As a bonus, this sort of code is great to throw into a modern game as something to stymie supercomputers or hackers, in case these things come up.