I'd take two discs to be honest. Fairway driver and a putter. Shouldn't be too much of a burden, running with one disc in your hand. (I won't say it, but you know what fairway driver and putter I'm thinking ).
I'm going Spider. Great disc that I can do a lot of things with. Struggle to find a place for it in the bag because I can find a lot of discs that do things better than the Spider, but no one disc does everything better than the Spider.
I've actually hit chains on approaches and long putts with it more than any other disc, which is where I try to keep it in my bag.