I'd want to be _certain_ I would not run out of juice or memory before the end of the trip

Making sure you have enough batteries and CF space is no different to making sure you have enough film with you. If you had a 1Gb micro drive and were taking photos that were 2Mb per file then you would be able to store 500 photos and would only need to make sure you had three charged batteries.

If you were doing this with film you would need 13 films and one set of spare batteries for the camera (just to be sure).

13 35mm films would take up far more space that two extra batteries for the digital camera, depending on the battery in question the fiilms could also be heavier...