I want to add more stuff to Doctor Stern's TC but I already have enough beakers and flasks. Suggestions?

Ochki might give you some ideas.

Hess is a bit of a unorthodox doctor, there's some things tho, like the Infectious Sample set, Flavored Poison set, Chemicals , mad science multi-tool,

Starscream. may give a bit more ideas mingled in with the plotting items. Upside Down Chemical Spiller 5000 is a neat one too.

It's technically an address sticker, but reminds me of the kind of labels you might use in a lab for samples.

Maybe as like a bunsen burner type object?

The typical school-child science project!

Lab equipment:

Safety equipment:

Other: [item=Nuclear Potion: Behind the Scenes]