How to keep sliced roast beef moist

[Bushmen's Smokehouse]

I'm new to doing roast beef for functions. I am worried about pre slicing (which I have to) and loosing moisture.
I have seen liquid in the pans at events, but not really sure what exactly it is, drippings, beef broth water.....
Thoughts, hints tips?

 

[centexsmoker]

If you have to pre-slice, beef broth in a warmer is the answer. You may be able to make it unique with a few spices and/or herbs depending on the flavor profile you are after.