Aside from folders for maps and the ability to import/export characters to CSV/XML files from/to your local machine, I don't have much to suggest in terms of new functions for Roll20. But an idea did occur to me the other day: a texture painting tool. Roll20 can fill in rectangles and circles with color and this does pretty will in a pinch if your party wizard summons a river of lava or a wall of stone. But drawing and filling a more amorphous shape is harder to do. What's needed is a texture paint brush with varying widths to paint in water, fire, tar/toxic sludge, etc onto the map in real time for your players to deal with.