I do have a bag with me, but similarly to 6Gman:
My bag usually has:
camera - several hundred pounds
lenses - several hundred pounds
memory card and spare - total ~£70 (plus unrecoverable photos on the way home)
flash unit - ~£40
filters - collectively ~£50
Spare batteries - 2× £20
Camera battery charger - £15
Camera clamp - £10
kindle - ~£80
high capacity powerbank - ~£30
Waterproof jacket - ~£30
heavy duty water bottle - ~£15
USB adapter and cables - ~£15
along with various small items that probably total another £15, a couple of cheap but sentimental items, and, sometimes, important letters, etc.
there is no way I'm leaving that unattended on a train.
Then prepare to be disappointed on Virgin Trains, which now show 'Available if unoccupied' a few minutes after leaving intermediate stations. I wouldn't move if I sat in a seat with nothing on it and displaying that message, and you then turned up trying to move me.