What's really important on sports pre- exercise forms?

+ allergies/asthma. Answering all questions to the best of your knowledge is always best. The questions asking about allergies (to medications, foods, bees, etc.) and any airway disease (asthma and the like) are critical to answer fully. Age appropriate questions regarding cardiovascular status (history of chest pain, high blood pressure, murmur, etc.) are also very important.
All of it. All the questions are important in the form. It was made to screen for the most common causes of problems during the sport participation and any positive answer (except a few) needs to be explain in detail. The doctor may need extra test depending on answers.