After a weekend of behavior issues with my oldest and seeing his progress report, I changed my mind. The Elf on the Shelf would indeed make an appearance this year. Since homework has become such a chore, I’m putting that Elf the work.
Addition with regrouping has become an issue lately, so Elf left extra problems. Other concepts that could be used is subtraction, perimeter, area, multiplication.
Elf couldn’t leave reading out. ¨I need a synonym for .¨ antonyms or rhyming words could be used.
Leave a riddle for your child to read.
Leave a homograph or homophone and have your child name the other. 
Sight words or if the teacher sends home a weekly newsletter, use the concepts they are working on that week.
For younger children, the Elf can leave a pattern with candy and have your child make another pattern. My 7 year old then counted and divided the candies evenly.
After he divided it equally, we then looked at them as an array. (2×8=16)
Leave a number and ask if it‘s even or odd.
Leave paint for your child to mix and make new colors.