Not done any endurance event of quite that duration myself as I'd be going shorter and quicker over a marathon. But thebasic needs can't be that dissimilar. I assume that you'll be carrying some kind of kit bag with you for the duration so you will be able to take supplies with you and your testing kit?
I never went as far as carrying my testing kit with me for a marathon, but I do always have a bunch of energy gels on me and I off the top of my head they would tend to work out as about the 20-30 g of carbs. Your options for eating and digesting whilst walking would be slightly more varied than when running, digesting solid food when running is never going to work well. :mrgreen:
I would think that you should be looking at a similar "diet" to regular walkers doing the hike, but with plenty of emergency quick acting carbs on standby such as Lucozade and gels, or even Kendal Mint Cake.
You should test taking the various things whilst on the move though and see how your stomach copes with them, I know that after 3hrs of eating gels I feel sick, but some people wouldn't be able to cope with one of them and I had to train myself to down them on the move. Stop, test, eat, hike should be workable for you though and a slight reduction in the previous days dose of Lantus may be worth trying out as well. I reduced my lantus by trial and error to deal with marathons, mostly by error though and I can't quite remember exactly which change worked the best for me previously now as I'm messing around with learning pump setting instead now.