A country of such diversity like Peru, it would depend on your itinerary on what you should bring.  For example: those planning adventure travel will need specific items such as tents.  Bring warm clothes for the sierra, light clothes for the Jungle and a combination of both for the coastal deserts that are warm by day and cool by night.  Items that might prove difficult to obtain in Peru include: your personal medical supplies, a strong money belt, sunscreen, good books in English and any electronic equipment tat you use.