+1 for multiple
memory cards, I went OS this year for 6 weeks and took 2 x 64Gb cards. Despite having 2, I only filled one. (around 2000 images shooting
Raw+JPG on 6D with 64Gb card....).
No additional storage was needed IMO, there's always a chance of losing the files, but that's also the case even while transferring to a backup device.
If I were buying again I'd buy 32Gb cards simply because losing the contents of a card is worse the larger the card.