I just had a short conversation with a young lady in which she claimed to be giving up diet soda for Lent. She said she would give up meat, but she likes steak too much. Same with chocolate. Now that’s commitment to a god!
As an affirmed atheist, I feel it’s my duty to sacrifice something important to me, but the sacrifice should be comensurate with my piety.
I, therefore, am abstaining from three bean salad. My abstention may last well beyond Easter.
You?
Self-denial. 
I’m giving up gardening until at least easter. Depending on the weather, I may have to give it up til Mother’s Day.
Employment. Looks like I’m giving that up for a while.
I’m a C&E christian. I gave up my salt-shaker. Back in January, I realized that I oversalt my food, and would like to regain some salt sensitivity for my taste-buds. Then lent came along = perfect excuse to finally do it. I’m still allowed to use salt-containing things, like ketchup, hot sauce or soy sauce, but no more salt as an additive to already seasoned food. So far eggs have been the hardest thing not to salt.
edit: I realize my answer was more serious then this thread required, so more to the OP: I’ve given up drinking low abv beers. Only the good stuff for me 
I’m giving up eating all meat. It’s a terrible sacrifice, but I got used to ten years ago when I became a vegetarian.
Reading books which are stupid wastes of time.
I’m still fine-tuning the details though–is it ok to read books which are only kinda stupid? How much of the book do I need to read before I can be sure that it is a stupid waste of time which I should not be reading?
Catholic Guilt
As a matter of empirical observation, it is beginning to look like I am giving up dieting.
We’ve decided to finalize the adoption of our newest cat, so I’m giving up any pretense of maintaining a really tidy home. Past experience tells me that this sacrifice will extend through the next 10 or 12 Lenten periods.
I’m giving up obedience of Catholic customs.
I’m giving up Judaism for Lent.
God help me, I gave up drinking alcohol.
I’ll give up murdering people, though maiming is still fair game.
I’m giving up Catholicism for Lent
I stopped eating red meat (for the most part) a few years ago. I always told myself one of these years I’m going to have an anti-Lent and eat nothing steaks and burgers for 40 days.
If I didn’t think that by now it would probably give me the trots for an additional 40 days, I might give it a shot.
Showering.
Back in 89’ I gave up going to church for lent. I enjoyed it so much I haven’t been back since.
I am giving up guilt.
Or die trying.
I’m giving up Lent for Lent. Seriously, why would I observe a custom that isn’t part of a religion I belong to?