Nylon cord has its place but it's terrible in many
boat applications. Especially the
cheap Chinese knock-offs that unravel if you looks sideways at them - and then dissolve in the sun.
I always carry some "tarred seine twine" from legendary rigger Brion Toss (who unfortunately passed away this year but his company carries on). Unlike paracord and other
cheap nylon - it doesn't unravel, knots never slip, doesn't chafe, is untouched by UV and looks extremely salty. The perfect thing to lash shackles, things to rails, and loose
gear. Despite the "tarred" name it is not sticky and non-marking.
I usually get the 42# cord. Scroll to the bottom of this page:
Brion Toss Yacht Riggers, Sailboat Rigging::Rigging Tools