There are pretty good deals on Amazon and eBay for bulk spools of line usually. You can get 30-40% off per yard, as compared to retail filler spools, and you don’t have to worry about coming up short when refilling a spool.
I have spools of line that are ten years old, including a three-pounder of Yo Zuri Hybrid 12# and multiple one-pounders of Hybrid, fluorocarbon, and braid. The line doesn’t go bad if it’s stored in a cool, dry, dark place like in a Rubbermaid tote in a closet.