Staying dry, mostly declining to conserve energy (2,3,5)
I believe the answer is:
on the wagon
'staying dry' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'mostly declining to conserve energy' is the wordplay.
'mostly' means to remove the last letter (most but not all of the word).
'declining' becomes 'on the wane' (I've seen this before).
'to conserve' means one lot of letters goes inside another.
'energy' becomes 'go' (go can mean energy or enthusiasm).
'onthewane' with its final letter taken off is 'onthewan'.
'onthewan' enclosing 'go' is 'ON THE WAGON'.
Can you help me to learn more?
(Other definitions for on the wagon that I've seen before include "Abstaining from alcohol" , "Off booze" , "Not drinking" , "Teetotal" , "Not taking alcohol" .)