Quick reply -
If you look in post #3 of the disABILITIES FAQs thread, there are some helpful resources, including some to ask questions about special diets.
Also, it used to be that the counter service restaurants all had the same things - chicken fingers, fries and hamburgers. Most also have healthier options including some things like fresh fruit. The restaurants with healthy options are marked with an apple on the park maps and CMs there can help you with the healthier dishes.
For the ride question, he should ask his doctor what the heart attack means for him. All the attractions with warnings are well marked with an icon on the park map, at a sign at the entrance and before boarding. I don't have time to post the list right now, but can tomorrow.