We'd need some in reserve for Kitchen Pr0n[1] whenever someone gets an n+1, too. But since that never leaves the jar, a small stock should last indefinitely.
[1] A uk.rec.cycling convention. On acquiring or significant modification of a bicycle, it should be photographed in the owner's kitchen and shared with the rest of the froup. Tradition dictates that a jar of Marmite be hidden somewhere in the photo, and that all follow-up posts be kitchen rather than bike related, until someone gives in and plays "chain's a bit slack" in a Mornington Crescent style.