So dietary restrictions are a pretty common feature of RL religions, often specifically regarding meat in some or all forms. There’s very little mentioned in official supplements for WFRP religions, so here’s my attempt at some suggestions. Even a single RL religion isn’t always consistent or equally strict for everyone, so I’ll try to list some options in descending order of stringency. Maybe the strictest is only for clerics/monks, or perhaps there are regional or sectarian differences (like between Tilean and Estalian Myrmidians). Note also that restrictions may not apply to pregnant women, small children, the sick, soldiers at war or travellers.
So here’s a list of the major Old World gods and suggested dietary restrictions of varying stringency. Those in italics are already in official supplements:
Dazh: Always eat in direct sunlight or by firelight
Esmerelda: Always sit down to eat at least four times a day / Never miss either breakfast
Handrich: No food not served by someone else / Never the cheapest or poorest food / Always leave leftovers to give as charity to the deserving poor
Khaine: Eat meat with every meal, the bloodier the better
The Lady: Commoners may not eat meat other than fish, fowl or rabbit, assuming their lord has given them a license to do so.
Manaan: Seafood only / No quadrupeds / The first fish caught each day must be thrown back in offering (ToS p.31)
Morr: No meat / … except on feast days or during funeral feasts / … unless freshly killed
Myrmidia: No food or drink native to Tilea/Estalia / Fast the day before a battle
Old Faith: No meat or cultivated crops
Ranald: Nothing you’ve paid for fairly / … with money you’ve legally earned
Rhya: No eggs or dairy, except for children and pregnant women
Shallya: No meat / no meal you do not share with another / no rare meat / no fowl
Sigmar: No beer that isn’t Dwarven or Imperial
Taal: Only meat you have hunted or caught yourself / no farmed meat or fish
Tor: No restrictions, since Tor has no organised cult.
Ulric: as Taal / No fowl (as considered unworthy)
Ursun: In Winter, eat only once per day in a feast beginning at sunset and ending by midnight / Always eat outside / Eat fish at least once a week but never meat and fish on the same day (RotIQ p.36)
Verena: No fowl
If I’ve missed something official, or you have any further suggestions, let me know in the comments.