While a person (or, in this case, character) doesn't [i]have[/i] to have a background in the military or similar fields in order to be capable of surviving an ordeal like this, I believe it certainly [i]helps[/i] and that the percentage of military personnel/similar among now (when the RP takes place, I mean) living people is far higher than it would have been before the outbreak. 

After all, while any accountant, waitress or football coach may be a natural survivor and combatant, every soldier is a trained one. It's just logical that, percentage wise, a greater number of people who undergoes applicable physical and mental training in their jobs survives for a longer time in a setting like this, and I think it's good that the cast in this RP reflects that.