First of all, this not my work. All credit goes to Zombull, the original author. That being said, they haven't updated it since 2014, so I'll attempt to keep it alive until/unless Zombull takes it back and/or tells me to take it down.
The original description:
Farmhand adds dynamic buttons on the screen while you are at Sunsong Ranch.
The buttons allow quick access to the Plow, Shovel, Bug Spray and Watering Can if they are in your inventory. If you do not have a given item, there will be no button for it. Also adds buttons for seeds that are in your inventory. You can even sell unwanted seeds at a vendor without having to open your bags.
When you leave Halfhill, any tools remaining in your inventory will be dropped. You can pick them up again at the farm. (You can disable this feature.)
Unfortunately, 9.0.2 broke this feature by making the destruction of items a protected command, so addons can't automatically delete items any more.
A special Crop Scanner tool will let you quickly find any plants you've overlooked that need special attention. (Very hand for the hard-to see Smothered and Runty plants.)
To move the buttons, hold SHIFT and drag a button with the left mouse button.
In the Interface Options panel, you can turn on/off tool dropping, turn on/off chat messages and sounds, turn on/off the portal shard buttons and control whether Farmhand automatically hides itself during combat.
I recommend using Masque (optional) to make your buttons pretty.