Related Clues:

• Get on in the bus for extra
• It's extra to get on in this bus
• 'It's for medicine if the boy comes back, by the sound of it (6)'
• The pill, if it's up to buck him up, by the sound of it
• Stimulus or boost
• Unexpected extra
• Coach catches on and gets a little extra
• Christmas green?
• See 8
• Transport's riding on extra payment
• Charge one penny for boost
• Medication provided when upset is a tonic
• Extra payment - reward
• Something adding stimulation
• Stimulus (sounds like a boy!)