Answer:
A precious gift, yet it has no end, no beginning, and nothing in the middle.
What ship has no captain but two mates?
Other terms for this handy device include doohicky, doo-dad, and whatchyamacallit.
It comes only before, it comes only after. Rises only in darkness, but rises only in light. It is always the same, but is yet always different.
What is always on its way but never arrives?
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.