It is reasonable to prepare yourself for extreme boredom, isolation, bad food, frustration, mild sensory deprivation, distressing noises from other prisoners, a bright light on 24/7 and being kept under constant surveillance. Remember, you can only be held for up to 24 hours (except for some very serious charges – unlikely in protest related cases). If you’ve prepared for the worst you may be pleasantly surprised!
If you are perhaps expecting to be arrested, bring along a book. Chances are you will be allowed to take it to your cell.
You might also want to ask the custody sergeant for a pencil and paper to take to the cell.