From a health point of view, an ideal day would include at least half an hour of exercise, 3 or 4 moderate meals, a good dose of fresh air and light, some work and some fun. Easy, isn't it?
Except that most of us don't get the chance to build our day as we'd like! But some things are under our control. For instance, starting the day with a good sized breakfast that includes some protein - an egg is ideal - gets you off to a good, high energy start. You can make yourself a nice lunch to eat at work and try to find time to cook a fresh evening meal several times a week - lots of nice dishes take less than half an hour.
A walk every day will do wonders for your health and happiness, especially in a park or at least near trees and grass. Also, you should try and have an hour most days that is just about relaxing - reading, listening to music (or walking or other exercise, which can be very relaxing.)
Finally, an ideal day includes a good night's sleep!