Useful Items
-photocopies of all your personal documents just in case you happen to misplace them or they are stolen
-leave a second copy of all personal documents in your home country
-a penknife is useful (goes in your main luggage)
-maglite or torch
-Iodine tablets and portable water filters to purify water particularly if traveling to rural areas and no bottled water is available
-insect repellant and insect spray
-sunscreen at least SPF 15

Essential Clothes
-lightweight waterproofs, hat and sunglasses for all parts of Argentina
-comfortable walking shoes
-warm fleeces and windproof clothing if travelling south
-lightweight long-sleeved shirts, long pants and hat if traveling to the north
-if you plan on dining out you will need a semi-smart set of clothes to fit in. Argentines tend to dress well

Important Medicines
-If you take prescription drugs, you are advised to travel with sufficient supplies for the length of your trip
-Anti-malarial drugs and mosquito nets if you plan to visit northern Argentina on the borders with Paraguay, Bolivia and Brazil 
-a traveller's first aid kit