Unnecessary spending — next gave a car, outrageous! (12)
I believe the answer is:
extravagance
'unnecessary spending' is the definition.
'extravagance' can be an answer for 'spending' (I have seen 'Excessive spending ' mean 'extravagance' so perhaps 'spending' could also mean 'extravagance'). I am not sure about the 'unnecessary' bit.
'next gave a car outrageous' is the wordplay.
'outrageous' indicates anagramming the letters (an outrageous spelling).
'next'+'gave'+'a'+'car'='nextgaveacar'
'nextgaveacar' anagrammed gives 'EXTRAVAGANCE'.
Can you help me to learn more?
(Other definitions for extravagance that I've seen before include "Profligacy" , "high consumption" , "Lavish expenditure (E, not Y)" , "Excessive spending" , "Overspending" .)