Magazines, rifle and pistol? Get more. I have lots, need more. Upgrade your firearms? Yes sir. More and better first aid supplies? Probably my most glaring weakness right now. Little pieces and parts for your firearms? I am ding pretty well on stuff for my rifle, pistol not as well. While I am a believer of the saying that the purpose of your pistol is to get you alive back to your rifle, you need to have the best, most functional pistol you can get.
It is easy to get caught up in the big stuff, the firearms themselves and expensive optics, but the accessories are very important. For a while I had rifles without slings so that is great as long as I don't need to carry them very far.
What about back-up knives? Knives can break or get lost. Same with flashlights and candles and....lots of stuff. Not everything is expensive. A pack of glow sticks is a couple of bucks. Kits full of springs and doodads that wear out and you can lose and need to replace are also not expensive and cheaper than having a non-functioning firearm because of a missing spring. These are just a few of the kits I have put into inventory over the last month or so. I also picked up some additional bolt carrier groups just in case.
I still try to get ammo where I can, so that I am not just replacing what I shoot but bringing in more than I shoot. Since the weather has been crappy as it always is in Indiana through April and I mostly shoot outside I haven't shot as much as I should but hopefully that is going to change.
Point being, you can still do something to improve your posture even when ammo is hard to get. No one is going to bemoan having too many magazines when they eventually get banned. No one is going to gripe about too much first aid material if someone gets hurt. Every day do something to get better prepared.