Stretchy base: perhaps Tupperware loses lid (7)
I believe the answer is:
elastic
'stretchy' is the definition.
(something elastic can be stretched)
'base perhaps tupperware loses lid' is the wordplay.
'base' becomes 'e' (Euler's number - base of natural logarithms).
'perhaps tupperware' becomes 'plastic'.
'loses lid' means to remove the first letter.
'plastic' with its first letter taken away is 'lastic'.
'e'+'lastic'='ELASTIC'
(Other definitions for elastic that I've seen before include "Stretch material" , "'Flexible, springy (7)'" , "Scale it (anag.)" , "Variable" , "Springy, like a rubber band" .)