Oh, is it a one off?
Pffft.
VT Bass DI and a headstock tuner. Fits in a gig bag and runs on batteries, power supply, or phantom power.
I think... OP says he is playing "a gig in Ireland at a meeting I'm attending."
I'm with you... a single pedal (DI / preamp) that can run on a 9v and a clip on tuner would get the job done for me.
If I HAD to have some effects, it seems like a fly rig or Zoom B3 would get the job done.