That's my KLR650 in the ADVrider thread. Carrying a twin tip and a couple kites isn't too big of a deal. You can just strap the board down under the kites at the rear of the bike. The board can go sideways or in line with the bike depending on what you prefer.
If you want to carry a surfboard you need a side rack. I'm not too keen to bother with a surfboard on a motorcycle myself unless it was just local low speed riding.