There is out of date and then there is super freaking old. Here are my loose self-imposed guidelines:
Oils are out for the most part. A Carlson of Nordic Naturals fish oil that is less than a month out I would be ok with but for the most part, I do not want 6-month-old krill or fish oil. I had a bottle of Mac Nut Oil from Swanson that was in the fridge from the day I bought it and it had an exp. date sometime in 2021. I just tossed it as it was absolutely rancid. If an oil kept in the fridge that has a year left on it goes bad I don't trust an expired one.
Dried herbs, isolated vitamins, and especially minerals are almost good indefinitely. For instance, tableted magnesium oxide is not going to magically convert to something else assuming semi-reasonable storage conditions.
Proteins that have all that creamer garbage added to them no thank you but otherwise, a few months is no big deal to me.
Bars: I eat a lot of these past dates but avoid ones with actual nut pieces as those taste rancid to me in a "fresh" bar. It is amazing how 10 seconds in the microwave and "refresh" an old quest like bar lol.
Now taste and texture definitely take a hit with stuff like pre-workouts and aminos. I have had some alphamine that tasted very different a year out of date.