I would suggest the most important thing you can pack - which weighs nothing - is patience.
For me, touring is a different style of riding. If you try to ride loaded for touring the same way you ride your road bike normally, I would guess you will soon find yourself frustrated at your 'apparent' lack of progress and with how tired you'll become from trying to, by habit, maintain your normal road pace.
If you normally ride with the dial turned up to 11, try to ride on your tour dialed back to 5 or 6. You might even consider yourself lazy or a slacker riding at that pace, but an amazing thing will happen: you will notice things along the way you never noticed road riding. I would also suggest planning stops along the way to purposely make yourself ride a 'tour' and not a 'race'. Pick out a couple of points or places along the way that interest you, and stop at those points for at least a few minutes.
For me it took some practice to set the dial to 5 or 6 and leave it there, and you might not be able to do that for the entire tour and you might not even like riding like that on your first tour. I would offer that it is worth a try if for nothing more than the sights you will see on your first tour that will create the foundation of memories for the tours that follow.