I did technical training to help fund a startup (had a co-founder). Trained approx 6 days a month (sometimes traveling). It helped make sure the bank account didn't drain quite as quickly. It was hard, but not as hard as a full time job.
> I'm a relationship manager at a commercial bank, what kind of part-time jobs can I get?
Virtual assistant? Maybe ask your current employer if you can go part-time (depending on how much they love you and if there's precedent)?
> However, I don't want to waste a year doing petty work on the startup.
In my experience there's all kinds of petty work at any startup, and a disproportionate amount falls to founders. They're kind of the catch-all utility players.
If you haven't done it yet and you have the time and opportunity, you might want to join a startup as an early employee to see what founders go through up close and personal.