I want to start by saying that I am in the Egg Industry, Eggs do not need to be refrigerated, they are done so to keep them fresh longer. As an egg ages the shell will loose it moisture and start to break down making the air cell large, When this happens it will change the grade of the egg from an AA to an A or A to B. The grade of an egg has nothing to do with the taste. Only how it stands up(meaning the yolk will sit higher on the white). coating the shell with oil will slow this affect.

I wouldn't worry about the eggs only from breaking. ALWAYS MAKE SURE YOU COOK THEM THOROUGHLY IN THE BACK COUNTRY.

http://www.incredibleegg.org/egg-facts/eggcyclopedia

Some nice facts all about eggs.

Nothing like some over easy eggs and toast while backpacking