[header] How to pack for a seven day vacation [title] Check weather patterns in your destination city. [step] If you're not leaving for a few weeks or even months, find a list of average highs and lows for the time of year that you're going to a particular place. [substeps] Search for averages on wikipedia; the site lists average temperatures in the " climate " section on most pages for countries, states, and provinces. 
You might also google the weather in a given city. For example, you can search " average temperature in chicago in april " to get results that will be helpful for choosing what to pack.