I would always buy a second-hand Netbook for a hundred pound and use that for travels. It wasn't as fancy or remotely as nice to work on as a MBP15" but then I can afford to lose a netbook but not a machine that cost over 2k at time of purchase.

For my last trip where weight was a concern I travelled with a USB chargable 40 dollar camera and a usb chargable iPod 32gb, for music and WiFi connectivity (skype, email, e-banking, downloading podcasts to listen to in my tent, the essentials).

I wrote notes on my iPod too and would write or type them up. But then I don't mind so much about blogging and I'm not going to sell or enter any competitions with my photos, so it was a good trade-off in terms of weight and not always worrying about having important stuff go missing.