There are times you will need to dress up. Know what is appropriate for the occasion. If you are going to a job interview or nice dinner, you should find out in advance if there is a dress code (i.e. jacket and tie, business attire, etc.). In times of needing to dress up, you don't need the most expensive clothes, yet they do need to be appropriate. For vacation, it's always good to include a polo shirt and nice khaki shorts or pants. Preparation in advance can save you embarrassment.