Sample code for medium article.

CompleteSandboxConfig.xml

<Configuration>
  <VGpu>Disabled</VGpu>
  <Networking>Default</Networking>
  <MappedFolders>
    <MappedFolder>
      <HostFolder>C:\Users\YOUR_USERNAME\Desktop\Scripts</HostFolder>
      <SandboxFolder>C:\Users\WDAGUtilityAccount\Desktop\Sandbox\</SandboxFolder>
      <ReadOnly>false</ReadOnly>
    </MappedFolder>
  </MappedFolders>
  <LogonCommand>
    <Command>powershell.exe -ExecutionPolicy Bypass -File C:\Users\WDAGUtilityAccount\Desktop\Sandbox\MainScript.ps1</Command>
  </LogonCommand>
  <AudioInput>Default</AudioInput>
  <VideoInput>Default</VideoInput>
  <ProtectedClient>Default</ProtectedClient>
  <PrinterRedirection>Default</PrinterRedirection>
  <ClipboardRedirection>Default</ClipboardRedirection>
  <MemoryInMB>0</MemoryInMB>
</Configuration>

ExampleSandboxConfig.xml

<Configuration>
  <VGpu>Disable</VGpu>
  <Networking>Disable</Networking>
  <MappedFolders>

    <!-- Basically this block copies Host folder a.k.a. C:\Users\Public\Downloads 
    To the desktop inside Windows Sandbox.
    -->
    <MappedFolder>

      <!-- This is a path from the host machine. -->
      <HostFolder>C:\Users\Public\Downloads</HostFolder>

       <!-- This is the desktop inside the Windows Sandbox. -->
      <SandboxFolder>C:\Users\WDAGUtilityAccount\Desktop</SandboxFolder>
      <ReadOnly>true</ReadOnly>
    </MappedFolder>
  </MappedFolders>
  <LogonCommand>
    <Command>explorer.exe C:\users\WDAGUtilityAccount\Downloads</Command>
  </LogonCommand>
</Configuration>

PackageManagerScript.ps1

# Download and install Scoop Package manager
# Note: This will not work if you disable the network access from
# Windows Sandbox configuration file.
Invoke-Expression (New-Object System.Net.WebClient).DownloadString('https://get.scoop.sh')

# Scoop package manager requires git to be able to install most software.
scoop install git

# Add extra buckets so we have more software to choose from.
scoop bucket add extras
scoop bucket add nerd-fonts
scoop bucket add nirsoft
scoop bucket add java
scoop bucket add jetbrains
scoop bucket add nonportable
scoop bucket add php

# Install Fiddler and Curl
scoop install fiddler, curl

ScoopBoxDemo2.cs

ISandbox sandbox = new Sandbox();
await sandbox.Run(new List<IScript>()
{
    new ExternalScript(new FileInfo(@"C:\Users\Scripts\StartBrowser.ps1"), new PowershellTranslator()),
    new ExternalScript(new FileInfo(@"C:\Users\Scripts\StartExplorer.ps1"), new PowershellTranslator()),
});

ScoopBoxDemo3.cs

ISandbox sandbox = new Sandbox();
await sandbox.Run(new List<IScript>()
{
    // PowerShell script as string to open notepad
    new LiteralScript(new List<string>() { @"Start-Process 'C:\windows\system32\notepad.exe'" }, new PowershellTranslator()),

    // Cmd script to open a browser
    new ExternalScript(new FileInfo(@"C:\Users\Scripts\StartBrowser.cmd"), new CmdTranslator()),

    // Bat script to open explorer
    new ExternalScript(new FileInfo(@"C:\Users\Scripts\OpenExplorer.bat"), new BatTranslator()),

    // Scoop package manager that installs curl and fiddler
    new ScoopPackageManagerScript(new List<string>(){ "curl", "fiddler" }),
});

ScoopBoxDemo4.cs

IOptions options = new Options()
{
    AudioInput = AudioInputOptions.Enable,
    PrinterRedirection = PrinterRedirectionOptions.Enable,
    Networking = NetworkingOptions.Default,
    VGpu = VGpuOptions.Enabled,
    // ...
};

ISandbox sandbox = new Sandbox(options);

ScoopDemo1.cs

ISandbox sandbox = new Sandbox();
await sandbox.Run(new ScoopPackageManagerScript(new List<string>() { "curl", "fiddler", "vscode" }));