transporting roast beef
It sounds like there's going to be some time between when it is cooked to when it is served, in which case the last thing you'd want to do is pre-carve it as it will dry out. Beef should rest after roasting, some chefs recommend roasting it as long as you cooked it, so don't worry if it takes 2-3 hours. 

The important thing is to make sure you keep it warm and as moist as possible, so what I would do is wrap it in foil and put it in the bottom part of a tupperware container. The foil will keep it warm while the container will catch any drips. You can put the container at the bottom of a bag for transport, just keep the bag open. It's not going to overcook as long as you take it out 10-15 degrees F below the target temperature. 

Just today I made a 2 rib roast and rested it by wrapping it in foil. The temperature climbed about 12 degrees after I took it out, and an hour and a half later it was still warmer than when I took it out of the oven, so the method works.