Why do they have feelings of foreboding when they are issued extra cheese and rum?

The servings of extra cheese have historically signaled rough times ahead.

Next day there was an issue of Edamer cheese. Each man gets almost a quarter of a cheese. In one way that is all to the good, for Edamer is tasty--but in another way it is vile, because the fat red balls have long been a sign of a bad time coming. Our forebodings increase as rum is served out. We drink it of course; but are not greatly comforted.