Little fellow to hitchhike covering miles (3,5)
I believe the answer is:
tom thumb
'little fellow' is the definition.
(I've seen this before)
'to hitchhike covering miles' is the wordplay.
'hitchhike' becomes 'thumb' (I've seen this in another clue).
'covering' is an insertion indicator.
'miles' becomes 'm' (common abbreviation).
'to'+'thumb'='tothumb'
'tothumb' enclosing 'm' is 'TOM THUMB'.
(Other definitions for tom thumb that I've seen before include "Panto character" , "Diminutive person" , "Tiny hero of nursery tale - digital?" , "Miniature hero of children's tale" , "Very little chap of English folklore" .)