Ok, so I looked at the new writable books, and there was something with the NBTagCompound. Does it store extra data for an item? If it does, can you please tell me how to use it.

Yes, NBTTagCompounds are used to store extra data for an ItemStack. They're not particularly hard to use.

 

You can give a tag compound to an itemstack using

ItemStack.setTagCompound(new NBTTagCompound());

 

You can add a list to your compound using

ItemStack.stackTagCompound.setTag("name", new NBTTagList("name"));

and then access this list using

NBTTagList list = (NBTTagList)ItemStack.stackTagCompound.getTag("name");

 

Once you've got your list, you can add compounds to it with

NBTTagCompound compound = new NBTTagCompound();

and add data to it, like Integers or Booleans using these

compound.setInteger("Integer Name", Value);
compound.setBoolean("Boolean Name", true/false);

 

And then finally to append this compound to the list, you use

list.appendTag(compound);

 

That would produce an ItemStack with a single list, which has inside it an Integer called Integer Name and a Boolean called Boolean Name.

 

Have fun