I'm not 100% striking but I do believe if you choose to strike then you are on the picket line for your shift! My mother is striking being a civil servant and is a union rep and said "I'll be home by 9am as my stint is 7-8.30am! We can shop then!"
When the nursery nurses were striking in 2004, friends off mine often took off shopping or going out for lunch. They didn't quite like me saying that wasn't what striking was about.