You may not find this terribly rewarding unless you're included here, so this is a good time for casual and random browsers to turn back before they get too caught up in the sweep and majesty of the proceedings and can't let go.
Most people know all about the Christian tradition of The Last Supper, in which the important items on the table are naturally the Bread and the Wine ('Do this in remembrance of me'), all recounted in the four gospels and 1 Corinthians. We've always been somewhat more interested in what else was on the table -- what were the Apostles actually having for dinner that evening? Passover lamb and fish are frequently shown, or at least hinted at, but we always seem to be coming up with rats.
This is the gem that first piqued our interest in the subject -- now that is clearly a rat. In the Museo de Bellas Artes of Seville, Spain, December 2011.
And this, in the same museum, the 'Sagrada Cena' by Alonso Vazquez in the late 16th century, in which the rat (if that's what it is) is somewhat bigger
In this 15th century picture by 'an unknown master', now in the Palazzo Bianco in Genoa, it's not clear what's in the dish, but it seems to be all stuck to the bottom [viewed in 2012].
This, by Tiepolo (c.1745) in the Louvre in Paris, looks more interesting than a rat, but . . .
. . . it's still not very helpful (detail), since most of it's already down the hatch [viewed in 2012].
An indigestible mass of something or other, labeled as by Ippolito Scarsella (Scarsellino, 1550?-1620) of the Ferrara School -- a very bad photo of one of his less well known pictures [viewed in the Pinacoteca Nazionale in Ferrara, 2013].
Along with the dinner rolls, what could this be?
This thing, too, appears to be a rat (by Paolo da Caylina the younger, ca. 1525, in the San Salvatore monastery or Brescia Museum) .
Still another rat (by Andrea di Bartolo, ca. 1420) in the Pinacoteca Nazionale in Bologna 
That thing, when the photo's been blown up a bit, appears to be the remains of a small fish (El Greco, ca. 1567, likewise in the Pinacoteca Nazionale in Bologna.
This is by Vasari, in the Casa Vasari in Arezzo [in 2015], and though it's not very clear, it too had might as well be a rat, sad little head and all.
More than one dish, for a change, but there are in total only eight very tiny fish, anchovies perhaps, by an anonymous artist in the early 14th century, in the Pinacoteca Malaspina in the Castello Visconti in Pavia .
Finally something a little more substantial for 13 growing boys than a loaf of bread, a fish, or a rat. This looks like meat loaf, or a broiled badger (by a painter from Cremona, late 16th century) [This fellow solved the classic 'halo problem' by just leaving the halos off. Except for Jesus, of course.] Also in the Pinacoteca Malaspina, viewed in 2015.
The Last Supper, solving the "where do you put the halo when they're facing away" problem, but Judas doesn't get a halo anyway. This is in the Museum Unterlinden in Colmar, with its fabulous collection of panels by Martin Schongauer (ca.1445-1491), a native son of Colmar [viewed in 2016].
Perhaps another rat, or maybe intended to suggest a lamb, with its head thoughtfully included alongside.
And this could just as easily be another rat or dog, but at least it's not got its head on it anymore. This is anonymous, another version of the previous one perhaps, from the Upper Rhine in about 1500, also in the Musée Unterlinden .
Still in Colmar's Musée Unterlinden, this, too, is clearly another rat, or a tiny dog.
There's nothing but bones left on this one, but apparently it's a bit bigger than a rat -- with the world's ugliest Judas Iscariot; this is attributed to a co-worker of Hans Holbein's, Basel, 1527, in the Basel Kunstmuseum .
Now we're talking; this looks like the better part of a small cow; let's call it a Passover lamb. It's by Bartolomeo Schedoni, ca. 1611, now in the Galleria Nazionale in the Palazzo della Pilotta in Parma .
That's definitely a rat -- a panel from an altarpiece by Giovanni Baronzio da Rimini, early/mid 14th century, in the National Gallery of the Marches region in Federico III da Montefeltro's
Ducal Palace in Urbino .
An unpleasant looking main course here . . .
. . . poor little thing. Passover lambs are frequent Last Supper themes (along with fish, and rats). This is said to be by Andrea Boscoli, late 16th century, also in the Ducal Palace in Urbino.
The front half of some baby deer or something, perhaps part of a lamb, in a fresco by Ugolino di Prete Ilario in the 1330s
in the Chapel of the Corporal in the Duomo of Orvieto [viewed in 2016]. Note the guest that Judas Iscariot has brought along to the party.
A mysterious main dish, from this distance . . .
. . . and not much clearer zoomed up a bit . . .
. . . and still totally unrecognizable. Cute little claws, though. By Il Romanino, 16th century, in the pinacoteca of the Civic Museum in the Eremitani in Padua 
This enigmatic mass, from an altarpiece, dated 1508-1511, by Francisco Henriques, a Flemish painter living in Portugal after 1500, will bear further investigation.
Some kind of ray fish, perhaps? With a rat on top? (in the Museu Nacional de Arte Antiga in Lisbon, viewed in 2017)
Here Jesus sits in front of a main dish which looks impossible to identify, perhaps a fowl of some kind . . .
. . . but in the whole huge fresco in the 'Corridor of the Last Supper' we find many main dishes set out, all similarly unidentifiable. The fresco is attributed to Bartolomeo Coda or his dad Benedetto, first half of the 16th century, and is now in the Museo della Città in Rimini. It's not a very intimate setting for a last supper, in an era before electronic amplification.
That thing is also unidentifiable, but close inspection suggests that either Jesus or the Sleeping Apostle is trying to hold it down. This crude piece of work is in a tiny chapel outside of the Castello della Manta near Saluzzo in the Piemonte region.
In addition to all of that fish, and the tempting bread rolls and fruit slices and the side of spinach, the main dish, if not exactly identifiable, looks really good (poultry, Passover lamb?). Judas' face is as expressive as you could wish for. This is by Daniele Crespi, 1629-30, now in the Brera in Milan [viewed most recently in 2018].
The Last Supper in one of the chapels. In addition to the traditional bread rolls, the main course seems to be a badger or opossum, something like that. Duomo in Bobbio, November 2018
The Last Supper in the Duomo of Mondovì -- the main course on the plate in the centre appears to be slab of liver, or foie gras.
An outlier, this one, from way earlier than the others -- it's an anonymous Last Supper mosaic from the early 6th century, we're told, from the Sant'Apollinare Nuovo Basilica, Ravenna, seen here in the cloister museum of the Chiesa di San Zeno in Verona. No rats, just fish!