If you work at it you should be able to shave at least a kilo off that 10.4kg, and your walks will be more pleasurable for it. In my case though, I guess I'm lucky that to start off with my ancient and still serviceable 75L pack is a great deal lighter than all modern ones.
Go through your list item by item (are you sure you included every single little thing, they all weigh something) and look online to see if there are any lighter alternatives that aren't going to break the bank. Even if you have no intention of replacing an item yet, make a note of what you've found for future reference, for you don't want all that searching going to waste.
I ought to stick this in the 'How To Help The Hours Pass By' thread