With today's lifestyle we cannot get all the vitamins and minerals we need from food

This depends on your lifestyle. Aspects of lifestyle which can adversely affect nutrient intake include:

physical inactivity
alcohol abuse
insufficient time to select or prepare food wisely
medication abuse
illegal drug abuse
cigarette smoking (which decreases taste sensitivity and opportunity for eating).

Usually the presence of only one of these factors is insufficient to adversely affect one's nutrient intake. But a combination of these circumstances is risky. It should be noted that stress in itself is not a risk factor for nutrient deficiency, yet this is a common advertising ploy to sell nutrient supplements.

It is preferable to modify lifestyle rather than to supplement your diet. If one does supplement the diet, it would be advisable to take a complete supplement with all the essential vitamins and minerals in amounts corresponding to the RDIs ( see appendix 2) and to take them for the shortest possible time, for example, just a few weeks.