AWS IAM policy with minimum permissions required by the packer post-processor amazon-import. I built the policy looking directly at the API calls made by packer.

PackerAmazonImport.json

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": [
        "s3:DeleteObject",
        "s3:PutObject",
        "s3:GetObject"
      ],
      "Effect": "Allow",
      "Resource": "*"
    },
    {
      "Action": [
        "ec2:CopyImage",
        "ec2:CreateTags",
        "ec2:DeregisterImage",
        "ec2:DescribeImages",
        "ec2:DescribeImportImageTasks",
        "ec2:ImportImage",
        "ec2:ModifyImageAttribute"
      ],
      "Effect": "Allow",
      "Resource": "*"
    }
  ]
}