I mean, you could start almost at the very top.

Skip hydrogen which is an obvious need and we're right at something that's not particularly helpful with either the creation or the sustenance of life. Helium has advanced use in MRI machines, and is fun in party balloons and squeaky voice tricks, but we got by for millennia without any of that. Relatively harmless otherwise, but not necessary.

Lithium? It does find itself in biological places often in place of more important things like sodium or potassium, but it's neither necessary nor completely worthless, I guess.

My vote, though, for the worst of the top of the periodic table: Beryllium. Toxic. No biological function except to cause problems. Helps make pretty crystals, but the same is true of lots of less harmful elements. In that sense then, completely worthless.