It's for breakfast: material detailed, including first of eggs (6)
I believe the answer is:
muesli
'it's for breakfast' is the definition.
(common breakfast food)
'material detailed including first of eggs' is the wordplay.
'material' becomes 'muslin' (muslin is a type of material).
'detailed' means to remove the last letter (the word must be end-less or 'de-tailed').
'including' means one lot of letters goes inside another.
'first of eggs' becomes 'e' (1st letter of 'eggs').
'muslin' with its last letter taken off is 'musli'.
'musli' placed around 'e' is 'MUESLI'.
(Other definitions for muesli that I've seen before include "healthy breakfast?" , "Cereal made with oats and nuts" , "Granola-like food" , "Swiss breakfast?" , "Breakfast mixture of dry cereals and fruits" .)