In Android development, what files should be committed to a repository?

GitHub maintains an official list of recommended .gitignore files at this public repository.

For Android you can find it here

Or just copy/paste :

# Built application files
*.apk
*.aar
*.ap_
*.aab

# Files for the ART/Dalvik VM
*.dex

# Java class files
*.class

# Generated files
bin/
gen/
out/
#  Uncomment the following line in case you need and you don't have the release build type files in your app
# release/

# Gradle files
.gradle/
build/

# Local configuration file (sdk path, etc)
local.properties

# Proguard folder generated by Eclipse
proguard/

# Log Files
*.log

# Android Studio Navigation editor temp files
.navigation/

# Android Studio captures folder
captures/

# IntelliJ
*.iml
.idea/workspace.xml
.idea/tasks.xml
.idea/gradle.xml
.idea/assetWizardSettings.xml
.idea/dictionaries
.idea/libraries
# Android Studio 3 in .gitignore file.
.idea/caches
.idea/modules.xml
# Comment next line if keeping position of elements in Navigation Editor is relevant for you
.idea/navEditor.xml

# Keystore files
# Uncomment the following lines if you do not want to check your keystore files in.
#*.jks
#*.keystore

# External native build folder generated in Android Studio 2.2 and later
.externalNativeBuild
.cxx/

# Google Services (e.g. APIs or Firebase)
# google-services.json

# Freeline
freeline.py
freeline/
freeline_project_description.json

# fastlane
fastlane/report.xml
fastlane/Preview.html
fastlane/screenshots
fastlane/test_output
fastlane/readme.md

# Version control
vcs.xml

# lint
lint/intermediates/
lint/generated/
lint/outputs/
lint/tmp/
# lint/reports/

don't add bin folder and gen folder. They are not part of your sources they are generated. In future remember that you add only files necessary to build and run your project, and binary and generated files are not.

Yet if you're not using any tool like ivy or maven you may want your lib folder to present. Often when you use a library project, you also need to commit it

The general rule of thumb is to not commit any file that can be re-generated, into the repository. Having said that, you may want to add your project.properties file to .gitignore as well (if it exists).