Pitch pastry into empty satchel (5)
I believe the answer is:
spiel
'pitch' is the definition.
(I've seen this in another clue)
'pastry into empty satchel' is the wordplay.
'pastry' becomes 'pie' (pie is a kind of pastry).
'into' means one lot of letters goes inside another.
'empty' means to remove the middle letters.
'satchel' with its middle taken out is 'sl'.
'pie' placed into 'sl' is 'SPIEL'.
(Other definitions for spiel that I've seen before include "Glib style of talk associated with salesmen" , "Plausible line of talk" , "Salesperson's speech" , "Glib story" , "Sales pitch" .)