Summer's beginning, pack and go away (5)
I believe the answer is:
scram
'go away' is the definition.
(scramming is a kind of going away)
'summer's beginning pack' is the wordplay.
'summer's beginning' becomes 'sc' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'pack' becomes 'ram' (synonyms).
'sc'+'ram'='SCRAM'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for scram that I've seen before include "Leave quickly" , "Vamoose" , "Leave hurriedly" , "Beat it, get lost, go away" , "Hop it!" .)