Looking for:
Zoom lens if possible
Pocketable
Large aperture
You won't get a pocketable large aperture, compact zoom.
An Olympus mju ii fits all but the zoom requirements but has an f2.8 35mm lens (similar to the Contax), so a bit on the short side unless you're right up front. But it's longer than the lens on an iPhone which seems to be the de facto gig camera these days. They're tiny and very good and sharp but are starting to get very expensive for what they are.
A mju 1 is as cheap as chips but loses 2/3 stop with it's f3.5 35mm lens.
The mju-ii zoom 115 has a zoom lens but it's very slow, especially at the long end. It is pocketable though!
Other 'quality' compacts tended towards wider lenses such as the Richoh GR1 with 28mm f2.8 lens or the Fuji Natura that had an f1.9 24mm (and both cost a lot of money now).
Bigger cameras like the Olympus IS-1000 had a 35-135 zoom but was only f4.5 to 5.6 and is far from pocketable.
A small rangefinder such as the Olympus 35RC are an alternative, with an f2.8 42mm lens but they're much less compact than, say, the Mju ii or the XA that Ko.Fe mentioned.
The XA is a bit fiddly for use in a concert though, it might be tricky to see the rangefinder patch clearly enough for accurate focus in poor light. An XA-2 is an f3.5 35mm, the same sized shell and uses three-part zone focussing but no manual override as it's auto only. Another thing to bear in mind is most of the compacts don't go up to ISO 1600 for their auto exposure. The XA and XA-2 for example go up to ISO 800. The mju ii goes up to ISO 3200 but I think that's with DX coding only, so you'd need to use Delta 3200 or change the code with a sticker to push, say, HP5+ to 1600 or higher.
Unfortunately you won't find exactly what you want as it never existed. You need a big lens for it to be fast and long and to cover 35mm frame size.
There were some 110 cameras that had long, fast lenses but you're stuck with tiny 110 film which is hard to find and harder to develop and print. And would look crap at high ISO too .
Most practical solution is to get something like Oly OM10 with 50 1.4. It is small kit to fit in the jacket pocket and it will give great results with ISO400 film pushed @1600.
Yeah, I'd go with something like that too. An OM-20 adds manual operation without the widget, but I'd be happy with a 50mm f1.8. It's smaller and lighter than the 1.4 and sharper (or as sharp) wide open. I'd put the camera in one pocket and the lens in another.