You can't even get in if you have asthma much less CF. The thing is that with things like deployment and being in the field you don't always have electricity, so doing meds or vesting would be impossible. Not to mention a ruck sack is about 50lbs already, if you tried to carry anything "extra" you couldn't handle it. Not to mention that I know some days my husband (army) barely get 1 MRE a day, a CFer just couldn't handle so little calories.