You can buy a badge for Pnut which unlocks some special features like File Storage, repost and follow E-mail notifications, and RSS feeds of your personal/unified streams for Pnut.
The intention behind the badge is to support Pnut directly and sustainably. The extra features are a thank-you. That is why above the minimum, you can choose to give more, and you have the option of displaying your badge on your profile.
For more, see the update at https://pnut.io/updates#2017-07-25.a.