I'd try to fit it fire, sharp, light, sound and water but the how is tricky.

Fire: A mini fire steel - maybe the striker part of a magnesium block or a couple of wooden matches and a cotton ball to go with it.

Sharp: A scalpel or a blade from one of those artsy exacto knives?

Light: A photon would probably be too big... Can't think of anything else that would be worth the space.

I once had a tiny brass whistle that would fit nicely and leave a little room but I'm not sure how loud it was. (Can't find it now to check.)

Water - a few micropur tabs and a breast mike bag?

Navigation - throw in a needle to use as a compass.

Signalling - polish the whole thing for signaling

Extras - wrap it in paracord, add some fishing line and then wrap those in duct tape.