I sincerely could not think of any food containing silver, so I had to Google it out. Turns out that eating silver is a thing, especially in Southeast Asia:
Vark, also called varak (also silver leaf, German paper), is super fine filigree foil sheet of pure metals, typically silver but sometimes gold, used to decorate South Asian sweets and food to make those look more appetising. The silver and gold are edible, though flavorless. (...) Estimated consumption of Vark is 275 tons (according to BWC-Beauty without cruelty data) annually (c. 2016).
However, it seems that not only werewolves and vampires would be badly affected by it (though regular humans could at least tolerate larger amounts of it):
Concerns have been raised about the ethical acceptability and food safety of Vark, as not all of it is pure silver (sometimes aluminium is used, which is toxic), nor hygienically prepared.
Every responsible dog owner knows that there is one human food that is poisonous to the vast majority of dogs: chocolate. Check this site for the reason, data, and a toxicity calculator. Supposing a werewolf weights at least as much as a human, they should be able to tolerate more chocolate than a dog, but they will still get intoxicated. Maybe the calculator helps you with ideas for how they would feel. The active component of chocolate that harms them is called theobromine, by the way.
Pet owners also know that caffeine is extremely dangerous to dogs, but it should not be so for werewolves. The reason is that the lethal dose of caffeine is about the same for dogs and humans: around 150mg per kilogram (about 2.2 pounds) of body weight. Pets usually suffer caffeine poisoning because they weight so much less than us. However, do notice that when caffeine is metabolized by a human, around 12% of it turns into theobromine (see the link I mentioned before), so I would expect a werewolf to at least suffer a little from a few cups of coffee.
Finally, most dogs hate citrus/citronella. Many dogs don't, though. I believe it's due to their sense of smell being so much more sensitive than ours. I would expect werewolves to avoid it like we humans avoid rotten food.
So, long story short: food products containing theobromine should be labeled so in order to protect werewolves, and both werewolves and vampires should avoid vark.