Old boy’s only travel equipment at first is old hat (8)
I believe the answer is:
obsolete
'old hat' is the definition.
(thesaurus)
'old boy's only travel equipment at first' is the wordplay.
'old boy' becomes 'ob'.
'only' becomes 'sole' ('sole' can be a synonym of 'only').
'at first' indicates taking the first letters.
The first letters of 'travel equipment' is 'te'.
'ob'+'sole'+'te'='OBSOLETE'
'is' acts as a link.
(Other definitions for obsolete that I've seen before include "No longer useful" , "Antiquated" , "being out of practice" , "Outdated" , "Out-of-date" .)