Mentally prepare Yankee companion opening soft drink (5,2)

'mentally prepare' is the definition.
(to psych up is to prepare psychologically)

'yankee companion opening soft drink' is the wordplay.
I cannot really see how this works, but
'yankee' could be 'y' (phonetic alphabet: alpha, bravo, charlie etc.) and 'y' is found within the answer.
'companion' could be 'ch' (Companion of Honour) and 'ch' is found in the answer.
'soft' could be 'p' (musical abbreviation for 'piano') and 'p' is found within the answer.
'drink' could be 'sup' (to sup is to drink) and 'sup' is found in the leftover letters.
This accounts for all the letters.
This explanation may well be incorrect...