Tip, take care of you feet. Stop immediately and tape any rub or hot spot. If you wait and power through, you will pay. Leukotape is the best tape ever.
About day 4 of going hard, you're body will hit a wall and your mind will want to do the same. Power through this wall and your body will accept the fact its going to have to keep working. From here the climbs seam easier and you start feeling stronger.
Always have a granola bar in your pocket. If you have to dig in your pack you're less likely to eat and you'll need the fuel. Same with water. Have a water bladder so you can keep drinking.