Artist tagged this with "K-On!", but I don't recognize either of these two.

They seem to be the girls at the school festival cooking yakisoba with Yui.

But I don't think they're anywhere near this busty.... heck I don't think Sawako sense is this close let alone a student...

It's not exactly rare for artists to exaggerate in that area...

The girls are definitely the school festival cooks though, everything else matches. I can't tell if the credits give their names, but they're probably more like "yakisoba girl #1" and "yakisoba girl #2".

They're just credited as 生徒 ("student") in the credits.

Danbooru needs a tag for characters that appear as extras!

extras?

We can go with extra for now.