I need to fire up an S3 bucket so my EC2 instances have access to store image files to it. The EC2 instances need read/write permissions. I do not want to make the S3 bucket
IAM role is the solution for you.
You need create role with s3 access permission, if the ec2 instance was started without any role, you have to re-build it with that role assigned.
Refer: Allowing AWS OpsWorks to Act on Your Behalf