No-hopers mislaid baggage containing uniform (4,6)
I believe the answer is:
lost causes
'no-hopers' is the definition.
(lost causes are hopeless people or things)
'mislaid baggage containing uniform' is the wordplay.
'mislaid' becomes 'lost' (similar in meaning).
'baggage' becomes 'cases' (suitcases).
'containing' means one lot of letters goes inside another.
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'cases' going around 'u' is 'causes'.
'lost'+'causes'='LOST CAUSES'
(Another definition for lost causes that I've seen is " people who can't succeed".)