thoughts on what second lens to get?

Hi everyone! Seeking some advice about my gear setup. I’m a documentary style photographer and am currently investing in a second camera body (mostly for backup purposes) and am at a bit of a loss as to what lens to get for it!

I currently shoot on the R5 w/ 28-70 f/2 as my main camera and then also have my EOS Elan II (film) camera w/ a 35mm f/2 lens on it. I haven’t really had a situation yet where i’ve felt a need for a lens other than my 28-70 That said, since i’m now going to be carrying a backup R5 body, I’m also in the market for a lens.

If you primarily shoot weddings on the 28-70, what other lens(es) do you find useful for your kit?

TIA!