Sunday was first originated on the seventh day of creation. God loved his work, and He wanted to sit back and enjoy it. He actually sanctified the seventh day, meaning that it was literally set apart. It isn't a normal day. After Christ's resurrection, the Sabbath changed from the last of the week to the first. So the importance hasn't changed, only the day. The day is still set apart by God for God.
This means that everything we do on a Sunday should be in meditation on God. This doesn't mean that you can't have nachos because you can't focus on God, but it does mean that you can't do certain things. What things? It differs from person to person, but the principle remains the same: glorify God on Sunday. Period, end of discussion.
Simply, if you can avoid things that will hinder your ability to meditate on God and praise Him, then don't do those things!
Let me put it in different terms: when you can have "best," why settle for "okay?"
I'll put it in a scenario, to make it easier for you to understand. Say you want to watch a movie. Not just any movie, but Ender's Game. And, as a little bonus to yourself, it isn't a sin to watch movie on Sunday, and you can even focus on God! (If only occasionally.)
What's wrong with this picture? Most people would say "nothing." But they would be wrong. Think about what your motive would be when you watch any movie, on Sunday or not: "this will entertain me." The operative word there isn't entertain; it's me. And that's fine. Scripture never condemns entertaining yourself.
But on Sunday, a day that God created solely to rest and to worship him, I want to watch a movie why? To entertain me. And focusing on God is an added bonus.
This is the messed up view of Sunday. It is perfectly fine the rest of the week, but not for a day specifically set apart, as outlined in the Fourth Commandment. As David put it in Psalm 119:36, "incline my heart to your testimonies, and not to selfish gain!" Should we not strive to be like David, in his more godly moments? On Sunday, our focus needs to be like David's focus in this passage. Not on ourselves, but on God.
A lot of activities are fine. And for some, there is no general rule. Others should just be dismissed out of hand. I'll leave it to you to decide what things go under which category. But keep this in mind.
Take example of Eric Liddell: he loved running. He said many times that when he ran, he felt the glory of God. He went to the olympics he was so fast. But his race was scheduled for Sunday. He refused to run on Sunday, and actually switched places with another man just so that he wouldn't have to run on Sunday. He loved running, shouldn't he be allowed to do what he loves? No.
Adam loved working. But he didn't do it on Sunday, because it was a day of rest, a day entirely set aside for God's glory.
This Sunday, maybe set aside some more time to meditate on God's word and reflect upon his glory. Cut back on the movies, read your Bible some more. But whatever you do, "remember the Sabbath day, to keep it holy" (Exodus 20:8).
Thank you for your time.