What to expect: simple chap with Yankee’s meanness (9)
I believe the answer is:
parsimony
'meanness' is the definition.
(I know that meanness can be written as parsimony)
'what to expect simple chap with yankee's' is the wordplay.
'what to expect' becomes 'par' (as in a phrase like 'that's par for the course').
'simple chap' becomes 'Simon' (nursery rhyme character Simple Simon).
'with' is a charade indicator (letters next to each other).
'yankee' becomes 'Y' (phonetic alphabet: alpha, bravo, charlie etc.).
'par'+'simon'+'y'='PARSIMONY'
(Other definitions for parsimony that I've seen before include "avoiding excess" , "Meanness" , "Tight-fistedness" , "Closeness" , "economic policy" .)