I still recommend splitting your cards up as well, cash is great but a lot of bookings etc on web for flights, rooms etc require a credit card... When I lost all mine and got ANZ to cancel them all and courier new ones over to my sister's place in the US i opened it up to find the only card they had sent was the American Express card, kind of useless as was flying on to Europe and then Africa and you can't get money out of ATMs with the Amex or book accommodation on hostelworld.com or hostels.com etc...
As for on planes i just usually stash anything i take out of my pockets (iPods, mobile, passport, etc) into the pocket in the seat in front of me and never had anyone make a grab for anything in over a 100 flights???