How to let Gimp remember canvas size and "Fill with"?

[Ofnuts]

Two solutions:

1. You define an image template, and then in Image > Canvas size you can select a template to apply its size. But this only applies the size, filling and such uses the dialog options.
   
2. Instead of Image > Canvas size you use the Crop tool, and check the Allow growing, specify a fixed size, and save this as tools presets if you want to reuse it later. Here again, you won't get an auto-fill.
   

OTOH it seems that the auto-fill you want is mostly a new image-wide background layer?