I always cycle out, so have one of my paneers with stuff ready to skate:
first aid kit (bandages, plasters, hydrogen peroxide, gloves, tweezers)
paracetamol/ibuprofen
voltaren (or whatever back and muscle pain relief I have at the time)
little cloth/towel to wipe ledges/wet benches with
skate tool
size 14 spanner
spare bearings, bolts and bushings
head torch
bin bag (in case rain comes/protect the board)
emergency snack (chocolate, cereal bar)
feel like half of the stuff is not necessary but it's all come in handy before