Three priority categories that I stock up on, whenever its affordable:
1. Rimfire. I can't load that myself.
2. Primers. I can't (safely) make them myself.
3. Lead. I can turn lead into projectiles, with several different methods; but I can't make lead.
Obviously, people that don't reload, cast/swage their own bullets, or have the motivation to make their own black powder have a lot more to worry about.
Trying to help out a friend in New Mexico that bought a Sig Mosquito for his daughter, in November, I spent about an hour digging online for .22 LR this morning. With very few exceptions that may not have been updated, the only somewhat reasonable things I could find in stock were some Winchester Wildcat 500-round bricks through a major gun parts retailer ($34(?)/brick), and some Aguila 500-round bricks through a popular reloading supplier (actually on sale, too).