Bound to eat last bit of cracker that's stale (5)
I believe the answer is:
tired
'stale' is the definition.
(I've seen this in another clue)
'bound to eat last bit of cracker' is the wordplay.
'bound' becomes 'tied' ('tie' can be a synonym of 'bind').
'to eat' is an insertion indicator.
'last bit of cracker' becomes 'r' (I am not sure about this - if you are sure you should believe this answer much more).
'tied' enclosing 'r' is 'TIRED'.
'that's' is the link.
Can you help me to learn more?
(Other definitions for tired that I've seen before include "Spent" , "Physically or mentally weary" , "Weary, jaded" , "Depleted of energy" , "Are American cars so" .)