Every Friday is an opportunity to remember how much Jesus has suffered for us. Lord, never let us forget how much you love us.
— Pope Francis (@Pontifex) July 26, 2013
Friday abstinence as a form of penance is the universal standard, but we are allowed to make an appropriate substitution. As with so many issues, many Catholics go straight from following a stricter rule to not doing anything at all out of ignorance, usually. This is due to the virtually absent teaching from our bishops and priests.
Remember, the provisions for abstinence were contained in the 1917 Code of Canon Law, which was not fully abrogated until 1983. Now, some terms were more laxly enforced, but the Second Vatican Council didn't do a thing to demand that Friday abstinence be relaxed. People simply chose to disobey, and this spread like wildfire.
Penance is not merely giving up something that is pleasing to us, although that is probably beneficial to us in the eyes of Our Lord. It is meant to draw us closer to Our Lord. The reason we abstain from the meat of the flesh-so poultry, beef, lamb, other livestock, and game- is because it leads us towards sins of passion. The ancients understood that men became more angry and morel lusty after eating a meal of flesh-meat.
It is another dimension to 'denial of the flesh.' It is not because it is a luxury. Actually, fish and dairy were more historically luxurious across Europe and the Holy Land.
I strongly suggest we bring this back as a mandatory practice. The Bishops of England and Wales have done so, though it is far from a universal practice in those areas. Again, poor teaching is rampant. But at least give bishops some law to use!