These are calcium, vitamin D, and perhaps zinc. We can get enough calcium and zinc from plant foods and we can make enough vitamin D from sun exposure, but supplements or fortified foods can be helpful sometimes. With all due respect to the naturopaths noted in the first question above, there is really nothing wise about adding meat to your diet. It simply isn't necessary and diets high in meat are linked to health problems. Iron is another nutrient that is hard to place in one of the categories above.
Vegans get plenty.
But poorer absorption means that we tend to have lower stores. For most of us, this doesn't appear to be a problem. It's not that hard. That's one of many popular ideas that has no real scientific foundation. It takes a severe long-term deficiency to produce noticeable symptoms.