If you do happen to turn it off completely. It's only two presses on the menu to get back to where you were, "1", to enter the Recent Books menu, then "1" again to open your last book.
I have to admit, I've been turning mine off overnight too. Had it three weeks now, reading between 50 and 100 pages per night and the battery has only just hit 50%. I want to see how long it takes to drop to 25% before I recharge then repeat keeping it locked rather than off.
Based on my current usage and battery life, I doubt I'd have to bother taking a charger with me on a two week holiday. Although since it's a usb charger/plug I'd probably take it anyway to top up my various other gadgets
