An Altoid tin can't contain bulky items such as a shelter, food and drink. Part of the idea is that the tin provides tools to help you acquire those things from the environment.

The emphasis is on items which are hard to improvise. For example, there's no real substitute for light, and if it's pitch dark it's hard to improvise a torch from found materials, or to do anything else, really. Hence a small photon light in the PSK. There should also be a knife, cordage, something to start a fire, and means to carry water, because those things, while possible to improvise in the wild, can be really tricky or time consuming.