Here is a list of services we've used you can use to make sure you don't forget anything in your cleanup.
It's also a good time to review all your learning :)
EC2 instances
Elastic Load Balancer
Launch Configurations
Auto Scaling Groups
Elastic IPs
Security Groups
EBS Volumes
Key Pairs
ECS environments (cluster, service, task def, ECR)
Elastic Beanstalk applications & environments
AWS Lambda functions
S3 files & buckets
RDS database
DynamoDB tables & indexes
ElastiCache cluster
Route53
API Gateway
Kinesis Streams
SNS Topics
SQS Queues
CodeCommit
CodeBuild
CodePipeline
CloudWatch Logs
CloudWatch Metrics
CloudWatch Dashboards
CloudWatch Alerts
CloudWatch Rules
CloudFormation Stacks
SSM Parameter Store
IAM User / Groups / Roles / Policies
That was a lot, congratulations!