Final answer:
An EMT should select an AED for its defibrillating capabilities and a bag-valve-mask for assisted ventilation during a cardiac arrest.
Step-by-step explanation:
If an EMT could initially take only two pieces of equipment to the side of a patient in cardiac arrest, the most crucial items would be A) an AED and B) a bag-valve-mask. An automated external defibrillator (AED) is essential because it can provide the necessary shock to help terminate the arrhythmia and allow the body's natural pacemaker to resume its normal rhythm. As for the bag-valve-mask, it is critical for providing adequate ventilation to the patient if they are not breathing properly or at all.