As an old trick-or-treater who got more than her fair share of those yucky chewy caramel thingies, I can suggest "dud" to describe them and other like-detested treats.
The first definition for "dud" fits this usage - per the Google dictionary:
noun: dud; plural noun: duds
- a thing that fails to work properly or is otherwise unsatisfactory or worthless. Ex.: "a high-grade collection, not a dud in the lot"
failure, flop, letdown, disappointment, loss-maker; More
informal washout, lemon, no-hoper, nonstarter, dead loss, clunker
"their new product is a dud"
For a little historical background (from the 1960's Midwest US), Halloween candy could be broken down by "quality":
Best - "full-size" candy bars!
Next Best - "fun-size" candy bars
OK - Other candy - includes Dum-Dum suckers, Smarties, Milk Duds (do not confuse with plain, old duds!) and finally...
Duds - Aforementioned chewy caramel thingies, apples, pennies, weird, wrapped lozenges with foreign words on them, anything else that is not candy.
Edit: In usage, "Hey! The Robinsons are giving out full-size Hershey bars! Don't bother with the Fluges' - they're giving out duds!"