I did the 40 mile Keswick to Barrow walk in May, my advice is this.
Go for lightweight shoes or boots, whichever is the most comfy. I wore trainers, however, by the end of the day I was wishing for something with a slightly thicker sole. Zinc Oxide tape is your new best friend http://www.firstaid4sport.co.uk/4sport-Zinc-Oxide-Tape-P4660/, if it starts to pinch or rub anywhere on your feet, tape it, I didn’t and paid for it. My feet hurt, but my hips and lower back hurt just as much. Core training helps, as does doing lots of walking in preperation. Salt will help you to stop cramping, so take lots of nuts, crisps etc. Drink water, lots of it, electrolyte fluid is better. if you’ve never used SIS, High5, etc before, now is the time. Don’t pack a bloody great rucksack, lightweight is the way to go, you’ll feel it by the end of the day. 70% of it is mental stength, you can make it, you just have to push yourself. Put a beer in the fridge for when you get back, or 2. You’ll have earnt it. Oh, and brag about it to your couch bound colleagues on Monday, most of them will be secrectly very jealous.
Good luck.