What I found most interesting is that all these sources not only advise their readers as to what kinds of food to place in their baskets, but also supply a kind of justification by explaining their symbolism. While various sources may differ in some details, they are overall fairly consistent. So here's my summary (you will find individual sources in the footnotes).
The foods that are always mentioned first are bread, eggs, salt and smoked meats (ham, sausage, etc.). As for their supposed symbolism, in the case of bread it's a Eucharistic and, therefore, Christian one: bread as the Body of Christ. Eggs (often brightly dyed or painted) are said to be a symbol of new or reborn life; and even though you might associate this them with Christ's resurrection, the sources avoid using the word "``resurrection" itself. Salt is particularly rich in symbolic meanings: hospitality, truth, meaning of life and even immortality. The meats, we shall come back to later.
Further spots are taken by: black pepper (if mentioned, then always in the same breath as salt), lamb, cakes and horseradish. The pepper is supposedly symbolic of ``harmony between humans and nature"; cakes (especially [[Good King Stanislas and the Forty Thieves|babas]], or Polish bundt cakes) stand for skill and perfection (which is why they should be always home-made), while horseradish is meant to be a sign of Christ's victory over suffering. It's getting more and more creative, I must say. When it comes to the lamb, it's not really the meat of a young sheep, but a lamb figurine, representing -- depending on the source -- Christ resurrected, victory of life over death and of good over evil, or meekness and gentleness. The figurine may fashioned out of butter, sugar, cake, chocolate or plaster (in the latter case, consumption not recommended). According to some source, you may also add cheese (possibly ''paskha'', an delicious Easter fresh-cheese dessert, although the illustrations feature slices of yellow cheese with holes instead), butter, chocolate (probably in the form of a lamb or a bunny) and water.
<nomobile>[[File:Dwa koszyki, dziesięć różnic.png|thumb|upright|Spot ten differences.]]</nomobile>
What may be surprising, even shocking to some, is that many of these justifications use such verbs as "``gives", "``brings", "``protects", "``provides" or "``guarantees". Apparently, the blessed victuals are not only charged with symbolic meanings, but also associated with magical properties. I've found most of such superstitious claims on the website of one Roman Catholic parish,<ref name=parafia/> but they crop up in other sources too. And so, bread and butter are said to bring good fortune and affluence; eggs provide fertility (a chocolate bunny may have a similar effect); cold meats bestow health and fertility, and affluence! Salt and water cleanse you of your sins, horseradish makes you strong and black pepper promotes healthy growth of your livestock.
The aforementioned parish website is also unusual in that it provides a list of things you should not put in your Easter basket. I'm sure it stems from the personal experience of priests who have seen all manner of things placed in their parishioners' baskets. The website mentions a few of the most common ones that the priests consider inappropriate: bunny figurines, alcohol, toys and mobile phones.<ref name=parafia/> Another curio comes from one major Polish web portals,<ref name=interia/> where Easter food-blessing tips are illustrated with a [https://tipy.interia.pl/132,0,tradycyjny-koszyk-wielkanocny.html diagram of an Easter basket.] Any Poles who sees it will probably ask, who puts a lit candle in their basket? It turns out, however, that the picture is a slightly modified version of an [http://www.carpatho-rusyn.org/easter.htm illustration] which first appeared in a magazine published by the Greek Catholic Union in the United States and pertains to Easter traditions of the Carpathian Ruthenes rather than the Poles.