Daily schedules fluctuate a lot. Between work, appointments, shopping, and after-school activities, every day looks a little different. In fact, this fluctuation isn’t restricted to day by day comparison. In the evening, you may find that your day ended up looking remarkably different than it did when it started. These fluctuations mean that things that you planned on doing may not have gotten done. When I'm pressed for time, I often cut my essentials - reading, prayer, and exercise. This approach is all wrong. Instead of seeking to save a few minutes from the things that you consider to be essential each day, look instead at your to-do list and defer a few tasks for another time.
The essentials are those things that you need to do each day in order to feel that a particular day was a success. As I previously mentioned, my essentials are getting some recreational reading done, praying, and exercising, typically in the form of walking. Whatever your essentials may be, these are the things that should be assigned the highest priority when time is tight, not cut the moment things get difficult. In fact, when you look at the activities that you consider to be essential, you might notice that they're the things that keep you balanced, motivated, and calm.
No matter what your day brings, do your essentials. They may not happen at the time or in the order that you planned, but they need to get done. When you look back on your weeks, months, and years, these essentials will be the things that move you forward as a human person, something that your to-do list won't be able to do. You may have to sacrifice some sleep, some project, or some chore in order to do them, but do the essentials no matter what.
The idea that a to-do list should get completely finished defeats the idea of a to-do list. The to-do list should be a compilation of every single task that you need to get done so that your list is in charge of maintaining that running list instead of your brain. You'll always have something that will need to get done. With that in mind, be comfortable deferring tasks for another day or skipping a few to-dos in order to make sure that you've got the essentials covered.
The temptation in time management is when things get tough to cut out the big stuff. Instead of going after your essentials, those things that contribute to a successful day, look at your to-do list and push a few non-essentials off to another time when you can give them the full attention that they deserve.