Carrier in second group (8)
I believe the answer is:
backpack
'carrier' is the definition.
(a backpack carries things)
'second group' is the wordplay.
'second' becomes 'back' (to second a motion is to back it).
'group' becomes 'pack' (pack can mean a group of things).
'back'+'pack'='BACKPACK'
'in' is the link.
(Other definitions for backpack that I've seen before include "Rucksack" , "It carries stuff" , "travel light?" , "luggage" , "Hike" .)