Knapsack weight carrying mixed bait (6)
I believe the answer is:
kitbag
'knapsack' is the definition.
(kitbag is a kind of knapsack)
'weight carrying mixed bait' is the wordplay.
'weight' becomes 'kg'.
'carrying' is an insertion indicator.
'mixed' indicates anagramming the letters.
'bait' anagrammed gives 'itba'.
'kg' enclosing 'itba' is 'KITBAG'.
(Other definitions for kitbag that I've seen before include "Serviceman's canvas pack" , "knapsack" , "Cylindrical canvas holder for soldiers' clothes" .)