It's a Shrove Thursday, called Fat Thursday in Poland today. Traditionally people buy and eat enormous amounts of doughnuts (p±czki) with rose jam filling and frosting top.
As Fat Thursday is the last occasion for feast making before Lent, which is a time of fasting, it’s simply a must to eat at least one doughnut to celebrate the day properly.
Be careful though! One “p±czek” has approximately 400 calories.