Spare halyard--what's the best line?

[JohnV]

I've got masthead sheaves for 3 halyards, so want to rig a light-weight line in the spare.
The boat is a heavy, 33-ft cruiser and I use 7/16" and 3/8" sta-set x for my halyards.
I'm not planning to use the spare as a topping lift, but instead for a potential emergency halyard, or for hauling heavy items aboard, or maybe for a trysail halyard at some point.
What's the best stuff to use in the third set of shaves for now? I've thought of simply using a 1/8" nylon messenger.
But then I wondered if something a little stronger would be better, so I could haul, say, my dinghy aboard with it--like maybe 1/4" double braid?
Then I figure, why not just splurge on a small-diameter high-modulus line that will be thin and light but strong enough to use as a halyard in a pinch if need be?
What do others do or suggest?
Thanks in advance for your thoughts.
John V.