How to create a Custom Dropdown List for Multiple Columns in Purchase Order Forms?

We are currently undertaking a task to enhance the functionality of our Purchase Orders and other correlated forms, Our objective is to create a custom dropdown (combo list) that spans multiple columns, akin to the functionality available in the Item field on Purchase Order. This type of enhancement is crucial for streamlining our ordering process and ensuring accurate data entry across various related forms.

To proceed with meticulous precision, we're seeking your expert guidance on the following aspects:

• Step-by-step instructions on creating a custom dropdown list for multi-columns in Purchase Orders and related forms.
• Best practices to adhere to and potential pitfalls to avoid during the implementation of this customization.