If you search the community for “Reflectix”, you will see some of us use the foil-lined bubble wrap as an alternative to ping pong balls. It’s easy to cut-to-fit most containers including insulating the sides of containers such as a metal stock pot.
I’d be concerned about styrofoam packing peanuts and possible leaching of stuff you don’t want. At least put some in really hot water to see what happens oven time before using them with your Anova. Many packing peanuts are now “bio-degradable” and dissolve in water. Which could mean a really gummy mess for your new Anova.