Replacement lillian cord is something you'll probably never need. The lillian almost never breaks and it is rare for it to get pulled off the rod tip. Having the lillian pull off does occasionally happen, though. It has happened to me twice and I know it has happened to other people (with rods of various different brands). I suspect it happens more often to people who use stronger tippets.
In any event, having some replacement lillian on hand can keep you fishing if the lillian does get pulled off or if you happen to break off the rod tip. You can use superglue for a streamside repair or epoxy (which is preferred) if doing the repair at home.
One package contains two sizes of lillian, and sufficient material to replace the lillian more times than you should ever need.