Answer:
Soldiers fight it but never changes.
What has black spots and a white face, is fat not thin, and helps you to win, but tumbles all over the place?
What grows when it eats, but dies when it drinks?
A mechanism to discover who is following you.
Other terms for this handy device include doohicky, doo-dad, and whatchyamacallit.
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.