Things to bring:
Warm clothes (and unwanted clothing for people who forget to wrap up warm)
Banner making equipment
Solutions to toilet problem
Contacts with groups, parties, unions, etc. for messages of support
First aid kits
This is not a comprehensive list and anything else you can think of that would come in handy please bring or list here for someone else to bring.
Also any skills anyone has to offer including but not limited to:
Any skills that can be put into a workshop, eg. Direct action, workplace organising, legal support, banner making, etc.