How to take off labels from plastic containers?

Score them and spray with either WD40, Goof Off or vinegar. Each will help to dissolve the glue.

Soak them in very hot water and a grease cutting soap.Then for the balance of the glue try some goo-gone

You can also try fabric stain spray, like Shout. I was able to get hundreds of stickers off of a bike helmet by spraying with Shout, letting it soak in a bit, and then wiping (maybe a tiny bit of scrubbing in parts) to get the stickers off. Worked great.

Use a hair dryer on the sticker. It melts the glue and comes right off!

Undo is a good product. It is sold at craft stores , like Michaels.

Goo Gone works great.