Might I suggest taking that Wenger swiss army knife seen in Carl's thread!
Other than that you don't need much... it's only two short days to your parents. If it were me I'd carry water, a snack, a tire repair kit (if you don't have laced wheels). I'd dress warmly in layers and have something to put stuff in like a gym bag or some reasonable facsimile strapped to the pillion. It's just not a long trip... not like you'll be on the road for weeks, so keep it simple and enjoy the ride.
