You definitely don't need Snickers bars. One place to start is Loren Cordain and Joe Friel's Paleo Diet for Athletes. On the Runner's World forums, there are tons of threads for marathons and ultrarunning on alternatives to crap food for fuel. Things like coconut water which has easily digestible carbs and electrolytes can be used instead of Gatorade for example. I drink that and mainline sea salt when I do long runs in the summer. I think it's amazing that your Dad is taking on this challenge! Ideas:

-Pemmican
-Coconut water
-Beef Jerky
-Chocolate sea salt almonds from Trader Joe's
-Hard boiled eggs (you can buy these in 7-11)
-Lara Bars
-Kombucha

Janine