You need to be as healthy and physically fit as possible because good health has a number of survival implications. For example, you may be able to get off meds for chronic conditions such as high cholesterol or diabetes (always a good thing during a disaster when medications may be hard to come by), you will be better able to haul your carcass out of a second story window during a fire or run from your neighborhood carrying a fully filled BOB, and healthy people tend to recover better if they are injured in a disaster or other type of accident.
Now having a routine exercise program can bore the socks off of you, especially if you are working out with no real goal. To "get in better shape" is too vague and unmeasurable to be very effective. The military has physical fitness goals in writing that recruits can strive for. The "Biggest Loser" has a competition to lose more than the other people to strive for. The runner has the New York Marathon to strive for. Get the idea? If you want to get in optimal (or even just better) shape, it is quite helpful to have a worthwhile goal to reach. A girl in our office is now working out with a group of beginners who want to enter a mini triathlon. Sounds like a big goal for someone who doesn't exercise but she is enthusiastic, she has a goal with a set deadline, and she has the group to help her be accountable. This is an excellent way to pull yourself back into shape. Consider setting a reasonable goal (ie: start off with a 5k run instead of a full marathon), work your way up to the condition necessary to be successful at your goal, then sent another, larger goal. You will thank yourself for this foresight should disaster strike.