The first year I ran it I peeled off most of the Adidas logo on the cap that I intended to wear and coloured the rest over with a black pen. It would have been easier to cover it with masking tape. It's so there will only be the logos of the kit sponsors on TV.
They sometimes provide a cap with the Comrades goodies. They have the last two years and this year I ran with the 2013 one on (since I had worn it before and knew it was OK). Other caps have to have the logo obscured. I have my buff around my neck and chuck water on it to keep cool