Light: I use a Fenix E01, which is expensive for your needs at $15. It's bigger and more expensive than the Ritter Pico LED but it takes common AAA batteries, and has outstanding runtime if you use Energizer Lithiums. It's also the closest thing to indestructible. The Pico probably has a better tint (many E01s have a purplish tint to them, which bothers some people).

Fire: I use a CountyComm peanut lighter, again, expensive for your needs at $11.50 (plus CountyComm's high shipping costs). A mini-Bic is an excellent choice; I secure the mini-Bics in my kits with a small cable tie under the button. I'd carry at least one lighter and one firesteel.

Knife or Multitool: Here's where I spend a good chunk of money. I consider a multitool a backup for a knife, not a primary knife in itself. A RitterGrip and a Leatherman Wave are the ones I'm most likely to have. An inexpensive keychain multitool can be had for around $15 and is better than nothing, though.

Navigation: A button compass is very inexpensive. I consider a map pretty important too, but I don't know how you can put one on a keyring.

Cordage: Paracord is bulky for a keyring setup, so you can get yourself a hank of good twine or tether cord if that makes more sense to you.

Signal: A good whistle (I carry a Fox 40 Micro) and a good signal mirror. Countycomm sells a nice small one in a cordura case.

Pill Capsule: Bayer is better for cardiac cases, Tylenol is better for (IMHO) everything else. I carry both but I use Advil the most. Chlorine dioxide tablets is preferred over iodine tablets. You might want to fill another pill capsule with TinderQuik.


Disclosure: I have no affiliation with any company or product mentioned here other than as a customer.