My core PSK items are in a BCB large kit tin that is 4.5" x 3" x 1". I really like it because:

- it gives me a little more room than an Altoids tin but is still compact enough to carry in a pocket if that's all the space I've got.

- it has an elastomeric seal in the lid that works pretty well. Still, I have 2 wide rubber bands cut from an old bicycle tube that I have put around the tin that really clamp it shut. The bands can be used as ongoing fire tinder if needed.

- like Izzy said, the rigid tin protects my chlorine dioxide tablets better than a soft case.

- as I posted here, the tin's lid makes a pretty darn good signal mirror. I drilled a hole in the middle to aid in aiming. I sealed the hole with some gorilla tape, and I put a PDA screen protector sheet on the inside surface to prevent scratches. I have a real AMK signal mirror in the kit but it costs no money, weight, or space to utilize the lid as a second mirror or a backup.

When I have space for more survival gear than just the tin, I pack that stuff and the tin in a USMC IFAK pouch which is about 6" x 6.5" x 2" and has MOLLE/PALS attachments.