Travel after nice surprise includes certain valuable objects (8,5)
I believe the answer is:
treasure trove
'valuable objects' is the definition.
(treasured objects)
'travel after nice surprise includes certain' is the wordplay.
'travel' becomes 'rove' (roving is a kind of travelling).
'after' means one lot of letters go next to another.
'nice surprise' becomes 'treat' (I've seen this before).
'includes' means one lot of letters goes inside another.
'certain' becomes 'sure' (synonyms).
'treat' placed around 'sure' is 'treasuret'.
'rove' after 'treasuret' is 'TREASURE-TROVE'.
(Other definitions for treasure trove that I've seen before include "Discovered valuables" , "asset to the government" , "stash?" , "valuable discovery" , "lot of valuable things" .)