For a king trip - I use the Timbuk2 Espionage backpack (as a carry on) which can take a lot - 4-5 lenses (prime and zoom), my Sony a77 and plenty of room for iPad/laptop and all sorts of accessories and have room for snacks, water and jacket/sweater. I also take a small sling (Thinktank Turnstyle 10 stuffed in my suitcase) to carry the camera and a lens or two while walking around my final destination. Worked great for a week in NYC. Had the glass I needed for each day but wasn't carrying around a ton of stuff while walking.