"Remember to Keep Holy the Sabbath".
What can you do on Sunday-what can't you do? (see the Cathechism) I tend towards the legalistic-I like clear and fast rules. But blind obedience to clear and fast rules can sometimes leave loving obedience and true understanding by the wayside.
John Paul II (of happy memory) wrote a apostolic letter On Keeping the Lord's Day Holy (Dies Domini). I recommend its reading to get a full understanding of all the Sabbath should mean to us.
As an aside, it appears John Paul II had read Chesterton-or at least had a common thought. From Dies Domini (No. 68):
In short, the Lord's Day thus becomes in the truest sense, the day of man as well. (emphasis in original).
and from Orthodoxy: (Chapter 5)
And only when they made a holy day for God did they find they had made a holiday for men.
The June issue of crisis magazine has article by Armstrong Williams which focusses on the "rest" aspect of the Sabbath. Read it here. In the final paragraphs (could be an entire aritcle unto itself) he makes a suggestion on why people are afraid to slow down and turn off the TV and cell phones on Sunday:
The Sabbath is often difficult. How could that be? Isn’t the day primarily about rest and renewal, about rejoicing and love? Yes, but it’s also about reflection, and about taking time to ask the important questions about how we are spending that time. I began this piece by mentioning how busy so many people tell me they are. They have cell phones on their hips, radios on in their cars, TVs on at home, and e-mails piling up at work. Many of us act as if all this activity is a burden—and it is a burden. But more than that, it is also a blanket meant to comfort us from the awesome—sometimes intimidating—power of silence and rest.
For some of us, the incredible pace of life is a self-induced state of denial, a ready excuse to avoid the hard questions. ...
We can't pray, we can't face God without silence and an uncluttered mind. (Isn't this why spiritual directors tell us to pray and meditate in the morning before we see the news, have read our email, or found out the problems we face that day at our jobs?)