Here is my short list of the essentials.

1. App stores

The GrapheneOS appstore only contains apps from the OS itself and a few more.

It also includes the Accrescent store, a minimal and very secure, but not yet fully released Appstore. Install Accrescent from here.

Be aware that Accrescent doesn't filter out apps with trackers or ads in them. Research them online before installing.

Obtainium

This is not a store, but the best way to get apps from various sources.

Here is the website, on modern phones you want the armv8a or higher APK. After downloading the APK, you need to allow "install apps from this source" for Vanadium.

When using Obtainium, Accrescent or AuroraStore you of course also need to allow app installs for those.

2. Basic apps

You can either search for these apps on the Obtainium app list or copy-paste the URL in the "add new" field.

Clock

Keyboard:

Gallery

Video Player: "Just Video Player" from Accrescent

Calculator

Mail

Thunderbird Android
Fair-Email (more complex and feature-rich)
ltt.rs (if your mail server supports the JMAP protocol)

VPN

MullvadVPN is currently (Nov. 2024) the only app passing code quality tests (memory tagging) on recent pixels
RethinkDNS may not work perfectly yet, but can use multiple Wireguard VPNs, Orbot and encrypted DNS
Orbot and InviziblePro offer Tor routing
i2pd and InviziblePro are likely the best for i2p routing.

Calendar

DAVx5 (if you fully trust your provider, often your mail provider)

Fossify Calendar

Or the Proton Suite

System tricks

Auto-Autorotate (only autorotate on selected apps)

Caffeinate (keep screen on for longer)

Clear Clipboard

Find SMS Code

LinkSheet to use the browser or app you want for every link.

SaveLocally comes in really handy when using the "Private Space" or work profile

SaverTuner if you want more extreme battery saving.

SD Contacts to backup your contacts to your storage. Warning, delete old backups after time!

Image editing

ImageToolbox

Snapseed from Aurorastore, APKPure or Aptoide. Use without network access.

Navigation

Convert Google Maps Links to Geo coordinates

OrganicMaps from Accrescent

OSMAnd~ or OSMAnd+ from F-Droid or the Playstore.

NeoStumbler to improve the non-GPS location service that GrapheneOS can use in the future!

StreetComplete for improving OpenStreetMaps easily

For speech navigation

sherpa onnx tts engines (there is a ton, filter by armv8a and your language. For english I like danny-low, for german I like thorsten-medium
RHVoice or eSpeak if you dont like the models

You need to enable the TTS engine in the settings.

Public Transport

Öffi
Transportr
webapps of your local service
often proprietary apps of them, you may want to avoid them.

find more apps

Add F-Droid Basic in Obtainium, install it. Search here for additional F-Droid repos that you can add within the app.

You may not want to use F-Droid to install the apps, but you can find them, copy the source URL into Obtainium.