Clue: 'All you can inhale' — final 20% off charge on coke, say, but not ecstasy (7)
Answer: LUNGFUL
Explanation: Definition: 'All you can inhale'
LUNG-e="charge" minus the fifth letter/"final 20% off", plus FU-e-L="coke, say", minus 'e' for "ecstasy"
 
"coke" is a fuel obtained from coal