Port 111 (UDP and TCP) is usually used for PortMapper, a Sun service usually associated with NFS (and usually necessary for the protocol to work properly).
Even if you're not running an NFS server on your system, you'll need PortMapper if you want to be able to mount NFS shares onto your OS X box (making your box an NFS client). If you don't plan to use NFS at all, you should be safe to turn PortMapper off.
Unfortunately, I'm not sure how to do this in OS X! Does anyone more learned than me have any idea?