I usually set up on a table with my lid closed too. My laptop is rather big (Sony K13) and actually runs pretty hot too, so I can't really do the bag thing.
Most of the small clubs that I tape in all have small tables available. Either that or we have scoped out the venue to the extent that we have key spots where we can have access to a Lazy Boy and a table (Lost Dog), or be able to set it up behind the sound board where it is drunk-free (The Haunt), or just far off to the side of the stage (Castaway's).
Regarding wandering beers, cover your laptop with a bar towel (you should have one in your gear bag regardless). I don't usually use one, but my buddy here in town uses a dry cleaning bag. It is clear enough to see your screen through and light enough to fold up and keep in your gear bag while maintaining the desired beer-free state.
...Kk