JohnnyK
Hardcore
http://www.reddit.com/r/dayz/comments/xpor1/til_that_you_can_access_your_inventory_vehicle/
Press "M" which will bring up your map (you don't actually need one) on the left hand side there is a bunch of options..
Hit "Units" and then click gear to the right.
Doing this you can Drink / Eat and move stuff around while in a moving vehicle.