I have used S3 bucket to save files. I used the SQL database from AWS. We use AWS Relational Database Services (RDS) and EC2, which is Elastic Cloud Compute. These are the three services I have used from Amazon.
S3 Simple Storage Service is used for sharing videos and photos. We created a system where we process and comment on content. For the backend, we save the files in S3 bucket, and provide that link to the frontend for displaying images. That is what we use S3 bucket for, as it is a simple storage solution.
I have been using Amazon RDS database service for 4-5 years. It is a normal Postgres installation, which we use for storage purposes.
Amazon RDS itself is a product offering different relational database services. It includes DynamoDB for NoSQL databases, as MySQL and Postgres for relational databases. I have used relational database services in Amazon which provides backup capabilities. If we miss anything, we can immediately restore from a backup to retrieve the data.
We use DigitalOcean mostly for RDS services and cloud-related systems where we deploy codes and run them using Nginx, as it is more economical. We also use it to extract data and manage Linux-related schedulers.