Could a large drywipe board behind you help? As items crop up, you write them on there; 'discharge AB', 'move DY to room 7' 'sort printer' - then with a different colour, you can step back and add the steps - 'call xy', 'need form 3489362i/b from zp'.
That way, it's out of your head, you can't be distracted by yet another email coming through, you can make a cuppa, stand back and see that three things are all waiting for one person to sort - and if somebody comes in and wants another thing done, you can add it to the board, they see it's been added but there are other things to do - and sometimes will take one look and say 'actually, I can sort it'.
A3 pads and sharpies or chisel tip markers work well for brain dumping as well.
It get you away from apps and computers and fancy procedures, you get space to think (and you can just stare into space over your cuppa and nobody will know any different) and it makes it more visual, rather than a scrappy list you might not be able to find when you need it. And you're more likely to remember things you've written in big writing in bright colours than typed in 11pt calibri or scribbled on the back of an envelope.
If they don't work, you could have an a4 ruled book for messages/things to do that holds the immediate contents of your head.
It's very satisfying to cross or rub things off, you can see at a glance what's outstanding, too - no missing the important thing that's been relegated to the bottom of the emails for three days in a row.