Catholicism and Christianity have quite a few differences. Christians (read: non-catholic) generally don't take part in lent.
No, Catholicism is a subset of Christianity. Christianity is believing in Christ's teaching.
And non-Catholics do take part in Lent, but they do it differently. "Giving stuff up" is normally a Catholic thing, and perhaps a few other groups do it. But other groups do have Lenten services and things.
I don't give stuff up. Basically, imagine if I came to your house and said I got you a gift. It's a brand new car. I also paid off your house, gave you money for college, gave you an all-expense paid trip to worlds, and got you a bunch of new cubes. You're really glad and you say, "Here, wait, I got you something too." And you go to your shelf and grab a candy bar.
Doesn't that seem odd? To try and repay me with something small for how much I've done is kind of an insult.
I think of Lent like that. You can't repay Jesus for dying for you by doing something small. He gave His life for you. The best way to repay that is giving your life to Him. Not by dying, but but living according to His Word. If you're Christian, you're already doing that, whether you're cubing or not.