On a more practical note...

When I was packing for this trip, I read dozens of websites for advice on what I should pack, and how much I should cart around with me versus how much I could buy along the way.

Here's an abbreviated list of what I ended up bringing in my 65L Eagle Creek backpack/daypack:

1 pair of hardy sandals (mortifying, considering I've spent 35 years making fun of Birkenstocks)

1 pair hardy trekking trainers/sneakers

3 ordinary T-shirts

1 T-shirt from Uniqlo with that heat technology

1 long sleeved shirt

2 bras (one sports)

8 pairs of pants (British pants not American)

5 pair of hiking socks

1 pair quick dying travel trousers

1 pair of jeans

1 pair of long johns 

1 fleece

1 woolen hoodie (thanks Nick!)

1 waterproof jacket

1 poncho

1 swim suit

1 sun dress

1 sarong

1 sleeping sheath

1 large & 1 small towel (both are those weird super thin quick drying towels)

1 foldable water bottle

1 money belt

1 roll of duct tape

1 waterproof backpack protector

1 tennis ball (to massage out aches and pains)

Toiletries etc (including toothbrush/paste, altitude medication, hairbrush, earplugs, padlock, flashlight, deodorant, bug repellent, tampax, iodine for water purification, burn cream, bandaids, small detergent, sink plug, ibuprofen, diarrhea pills etc etc)

Passports (UK & USA), photocopies of passports, two credit cards hidden in different locations, about $300 in cash (also hidden)

1 Mac book air

1 Canon video camera

1 Sony still camera

1 I-pod touch

1 Kindle

All the chargers and cords to go with the above

Three small notebooks (a diary, a journal and a general scribble book)

1 copy of South America on a shoestring

1 small spanish/english dictionary

So far, I have not had to use the sleeping sheath, the backpack protector, the towels, the water bottle, the purification tablets, the duct tape, the tennis ball or (thank god) any of the pills for various ailments barring the odd ibuprofen for a hangover. The laundry kit also remains unused, it's been easy enough in Chile & Argentina to drop off small loads at various laundromats.

I was very grateful for the poncho, waterproof windbreaker, long johns, fleece and hoodie in Patagonia and Tierra Del Fuego, and the macbook & I-pod & Kindle are brilliant, but by far the most useful items I packed were the smallest. The padlock, the flashlight and the earplugs (hostels have incredibly thin walls, and dorm-mates can be super noisy.)

The one thing I totally blanked on bringing, because I never wear them at home, were pajamas! So far, as previously mentioned, I've been combining long johns with a T-shirt when I sleep in dorms. I'm planning on picking up a cheap pair of leggings to remedy the situation. I'm also going to pick up some flip-flops, which are much easier to wear around hostels than sandals and which might provide protection in the shower.

I'm pretty sure almost everything else will come in handy at some point on this journey, especially once I get into Brazil, Venezuela, Colombia, Ecuador, Peru and Bolivia, with all the different climates/water sources/possible maladies I'll encounter. Hopefully I'll have a more definitive list by the end of the trip of what worked for me if anyone else is thinking of spending a few months in South America.

And if you are thinking of such a trip, a quick warning. Everything has been WAY more expensive that the most recent travel books had me believe (my edition of South America on a Shoestring was published in March 2010). In Argentina, almost everything is nearly double what was listed and the bus prices have almost tripled. In many cases, it is only slightly more expensive to take a plane over a bus. Chile was never going to be cheap, but it was also much pricier than guidebook guidelines. And if you are traveling on a US or Canadian or Australian passport? You have to pay reciprocity fees to enter a lot of countries (because the US, Canadian, Australian governments charge Latin Americans when they enter the US, Canada or Australia). You'll probably need a visa for Brazil too. I'm lucky to have a UK passport, and I fortunately over-budgeted for this trip. But I've met a lot of travelers who are having to curtail their trips because everything is so much more expensive than they (or I) thought it would be.