Localstack S3 UI
At the moment Localstack does not offer a UI to view content stored in S3. Assuming you're running localstack via docker and have provided the correct envs and volume mappings. Localstack will store the S3 content in this file /tmp/localstack/data/recorded_api_calls.json.
This docker image when used with Localstack, will parse the above file and generate a UI.
More information is available here to get set up.