Task:

multi-vitamin for trace elements and micronutrients

You should be taking a vitamin every day so that you get all the trace nutrients and elements that don't happen to be in all the food you are eating that day.  Most of what is in the vitamin should be part of your normal diet already.  But remember, you are taking a supplement for the things that don't happen to get enough of based on rotating meal plans that probably don't contain 100% of everything you need after cooking damage, things that block absorption of other things, etc.  Your body will take in the vitamins and minerals it needs, and you will pee out the rest.

Because vitamins are very personalized based on current diet plan, gender, and athletic needs, you will need to find something best for the current you.  Keep these things in mind as you shop:
 
- Males/Females/Young/Old need more of some things and less of others.  For ex, men should beware of too much iron, especially if you are already eating tons of red meat.  Choose a vitamin without iron unless you know you need it.
- cheap ones can contain useless synthetic variants. Get a quality brand with vitamins in the natural state like they are in food.
- don't get a  "1 a day".  Your body absorbs smaller servings better, spread out with each meal.  Take part of a dose with each meal.
- try and stick to brands that don't cram in much more than vitamins and minerals.  You should be taking a vitamin only to make sure you are getting everything your body actually needs.  If you want to take supplements that are not vitamins or minerals, get those directly in forms that are high quality. 
- don't worry about taking the full dose.  If you are consuming a well balanced diet, you may be fine taking just one of a two or three pill dose on days where you are eating very balanced and more on days where you didn't happen to eat enough greens.

Get a vitamin and take it every day.