To make marathon playing sessions easier on your mouth and to soften your sound for classical playing, buy a pack of cigarette papers. Before you play, fold one in half, put it in your mouth and let it soak for awhile. Then fold it across your bottom teeth. It will form a buffer between your teeth and your lip, making playing more comfortable. It also takes some of the edge of your sound, which may or may not be a good thing, depending on the gig.
I used to use wax when I was in marching band as a kid. Boy would my lips bleed from all that playing!