What Should I Wear For My First Day Working At A Thrift Store?

I've been hired as a volunteer for my local thrift store, it's not like... quality... so I don't know if it would be acceptable to just wear a nice tee shirt and jeans since I'll likely just be packaging things, or should I wear a nice cardigan? How much do I have to dress up for this job? The only worker I've seen just wore a long sleeve tee shirt with a short sleeve on top, and a necklace. What do you think I should wear?