On my pockets:

Phone, wallet which includes ID, a disposable card (to open doors if someone forgets the keys inside), cheap wired hearbuds (in case I forget my headphones), a flash drive, transport pass, a debit card with 8 euros balance, and 3 euros cash.

On my neck:

Headphones

I sometimes also bring my camera bag:

Camera body, 2 lenses, field recorder, dead cat and extra batteries.