I don't usually take multivitamins. I've read that it's best to get nutrients from our food, as our bodies are more likely to absorb them. The vitamins have the nutrients, but it's really unclear how much we absorb (from what I've read). I do try to eat a variety of foods to get the nutrients. On days when I don't think I've done a good job with my food choices, I do take a multivitamin.
I do take a calcium supplement (or 2) every day (with vitamin D). I often technically get the right amount of calcium in my food, but I know that you need vitamin D to absorb it, and that caffeine inhibits the absorbtion (much of my calcium comes during breakfast, when I'm also drinking coffee)...
And then, frequently, my head wants to explode trying to keep all this in mind as I go about my day trying to figure out what and when to eat!!