Payment Field: Ability to have own options saved as a Preset

While working with the purchase order widget, I noticed there is a field that says "Populate Options from Presets". This has a drop down with items like "Color", "T-Shirt Size", "Print Size", etc. Is there any way for me to add my own presets to this drop down? 

Yes, there's a way for you to add yours. Just set it to NONE then add yours on the fields below it:

And if you want different prices per option, just set the SPECIAL PRICING PER OPTION to YES.

Complete guide: How-to-Add-Options-to-Payment-Forms 

Looks like you pressed submit before you finished your answer :) The guide you linked doesn't tell me anything I didn't already know.

How do I get those added to the preset drop down, so I don't have to retype them the next time I have a similar product? 

Sadly, there's no way to add your own preset that can be used with other products. You'd have to set them up and manually type them every time. I understand it's a tedious process but the presets we have for the T-Shirt sizes, Color, Print Sizes are sort of like templates for the most commonly used options in conjunction with selling products.

What I can do to help is to elevate your thread as a feature request. Please keep in mind that there's no assurance whether this will be implemented. It will highly depend on the viability of the feature, the amount of similar requests we get, along with the workload of our Developers.

We can't give you any timeframe but we'll keep you apprised on this same thread when there's an update.

For the time being, the only way I could think of to lessen the workload is to duplicate your products, as this also duplicates the options as well.

Okay. Thank you.