A blouse is a great alternative to a typical stiff shirt; it's less 'banker' and more feminine whilst still looking smart. Adding a pair of jeans gives the outfit a casual edge, but when wearing jeans make sure you stay away from trainers/tennis shoes! Both of these items together is too casual.
A simple vest top can be smartened up with a blazer jacket, but isn't overly smart like a shirt and blazer. Again a pair of jeans is perfect with this outfit, but if jeans aren't your thing then black trousers should work fine. Don't overdo it on the accessories - pick one or two items that stand out, but aren't in your face. A collar necklace is ironic but fits well, looking both smart and casual. If you have to walk far then try to find pair of shoes that are comfortable, but are still dressy. Ankle boots work great.
When choosing a bag, make sure you have enough room for all of your 'interview items'. The interviewer should tell you what you need to take along. A structured handbag is ideal, as well as a satchel. Avoid backpacks! Whilst they're in fashion at the moment I still feel like they are too casual.