I'm going to be going on my very first metric century this weekend. One of the issues I've dealt with on long rides (50-55mi) in the past is running out of energy and water, so this time I made sure this route passes through a few small towns that have food/water for sale.

I noticed one of the towns I pass through has an Arbys on my route, and I was wondering if it would be a good idea to stop in and get a roast beef sandwich with cheese? Here's my thinking:

Roast beef: protein and potassium
Cheese: sodium and fat
Bun: carbs for energy

It seems like it would be a good idea to me. Is there anything I'm missing? Is this a bad idea? Are there better alternatives?