The only summer hat left – it’s a bit much (4,5)
I believe the answer is:
last straw
'the only summer hat' is the definition.
The definition suggests a singular noun which matches the answer.
'left it's a bit much' is the wordplay.
I cannot really see how this works, but
'left' could be 'l' (common abbreviation) and 'l' is present in the answer.
'it's' could be 'ts' (abbreviation. e.g. in 'tis) and 'ts' is present in the answer.
'a' is within the answer.
The remaining letters 'straw' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for last straw that I've seen before include "Something that finally makes a situation intolerable" , "One too many perhaps" , "The final provocation" , "That which broke the camel's back?" , "Back-breaking assignment" .)