If my quick bread recipe calls for an 8x4 loaf pan, what size paper pan should I buy to make giftable loaves?

Hi Jen - do you mean you want to use your recipe to make mini loaves? This is a helpful post for making your recipe fit your pan size: https://food52.com/blog/13239-how-to-make-your-baking-recipe-fit-your-pan-size

Don't know size of your store's paper pans.
Use one of these charts...compare the paper pan by size or volume (check the label)...a standard 8x4 pan holds 4 cups.
You can go from there.
https://www.browneyedbaker.com/how-to-convert-pan-sizes/