So you said leave for the day so that's like a typical work days? I am usually carrying a laptop with is 19V input so its power supply, and usually just a phone and BT headphones. To keep the phone working for the worst possible day then I carry the Powercore 10000 as it has the most power for weight/volume and would do for the worst day, and then also carry the Powercore Slim 5000 in case the 10000 were to go bust. I carry the Powerport 2 and a USB-C and USB2 cable.
Less typical days I'd just traveling with just my phone and only my pockets and then I carry just the Slim.
Even less typical I'm moving around aiports, hotels and i find I prefer to not have laptop and just move around with a large Tablet. Then I tend to carry the Powerport 5 USB-C to charge my tablet+phone+battery+BT and then carry also both the 10000 and 5000 for same reasons (a bit of redundancy and can charge them both concurrently for 4A of input).
I'm getting delivered the new Powercore 26800, not sure what I'm going to do with that. I have had the odd day where I was flying a long flight and the in-power seat was broken/missing and I had drained all of my 15000mah and was then slowly running down my internal gadget power but never actually ended up with evething flat. To handle that situation getting worse I'm not sure what I might do, either add another Powercore 1000mah or the Powercore 26800mah. Its a weight vs worst-day-possible situation.