The customs immediately preceding the fast are consequences of the fast's rules, and they make sense only in that light.
Prohibited foods that would spoil had to be used up. Eggs, milk and fat were made into pancakes, which is the origin of Shrove Tuesday in Britain and Ireland. Eggs laid during Lent could not be eaten, and preserving them by hard-boiling, and then decorating them for the feast at the end, is the most economical explanation for the association of eggs with Easter, an explanation internal to Christian practice, and considerably better supported than the fertility-symbol account usually offered.
Carnival, from a Latin phrase most plausibly meaning the removal of meat, is the same logic on a larger scale: a period of licence and consumption ending abruptly at midnight before the fast. The elaborate carnivals of Venice, Cologne, New Orleans and Rio are all calendrically tied to Easter and move with it.
Shrove comes from shriving, confession, which was expected before the season began. The Tuesday's English name records a sacramental obligation that the pancakes have entirely eclipsed.
The season's other characteristic practices are almsgiving and prayer, which patristic and medieval writers consistently name alongside fasting as the three-part discipline; reducing Lent to the food is a modern narrowing. Many Protestant churches abandoned Lent at the Reformation as unscriptural and a number have taken it up again in the last fifty years, often as a season of reflection without the dietary rules.