Yoreh Deah permits milchigs bread if there is a siman on the loaf. The kashrus agencies would rely on the D on the wrapping. Very iffy. Most reputable kashrus agencies do not do this anymore for bread.
The gemara says it’s sakanah to eat fish and meat together. It’s not a kashrus issue but a sakanah issue. Rav Dovid Feinstein Shlit”a agrees to Rav Shachter partially in that it’s probably not applicable today, but he argues in that he would still keep to the exact case of the shulchan aruch. So it’s batul beshishim, it’s only cooking together that is the issue, and it’s fine to drink omega-3 oj with meat.
The gemara says that you can’t leave peeled eggs, onions, and garlic overnight due to sakanah. The shulchan aruch does not mention this halacha. Some poskim argue that it’s not relevant anymore, as it’s no longer a sakanah. Others say it’s relevant but only as-ism like Rav Dovid Feinstein Shlit”a. There is a kulah relied upon that it’s not an issue in large quantities, so you can buy peeled garlic from a store. Not too many people are makpid on this halacha anymore. Chassidim are makpid on this halacha for their products.