Hey there, I have a similar issue at the minute, will be roughing it in Malaysia for 4 weeks. I decided to take my dSLR and most versatile zoom lens, along with a small compact digital also. That way at least I can accomodate for most shots, and most outings depending on space I have in my bag at the time.
I think the trick is not to go overboard, but if you think you really need it then take it... I set everything out and said "right, which can I leave here without kicking myself in the shins should I need it..." For example, as much as I love my 50mm prime, my 28-105 will cover this focal length and more, maybe not as well or as quickly... but its staying home! I've found that changing lenses and fiddling with bits in pieces whilst for example camping, or being in dirtier conditions that normal can lead to getting muck into your camera and lenses too...
Also if bits and pieces are small it might be worth squeezing them in, better looking at it than looking for it!!
Obviously with your friend having a pickup he can lockand a tent to keep things in he can take lots more stuff than me (where I'll be sleeping under the stars probably!), and with exciting national parks etc on his doorstep he'd maybe be a fool not to! I think its just a case of being realistic about what you'll need...
). Now this friend has a lot of equipment. He will be going in a full sized pickup (4 door shortbed). And a small pop up camper. How much equipment would you take?
