More can always be said on this matter, especially since the previous posts below are all from the British side of things; the French and German POVs of trench life on the Western Front remain ground so far little-trod on the sub. If anyone's got insights, this might be your chance!

For the Brits, u/NMW has two old but still excellent posts on this matter. One post examines the daily life of a British infantryman at the front, which also looks at food along the way. Another is a deeper look at food, and rations in particular.

I also highly commend to your attention the WWI section of the FAQ, for a great deal more information about the war in general and conditions in the trenches.