I blame Doug Ritter.
He fubar'd big time when he designed the RSK Mk1-3 without a built in time/space warp for us to stash the rest of the kit in.

Seriously:

To me an Altoids tin kit is the equivalent of a hollow handled knife kit.

In mine I have:
5 needles (assorted)
2 plasters.
1 Silva S.E.R.E. compass (luminous).
1 single edged razor.
Assorted split-shot.
6' cord.
1 spark-lite.
13 tinder-quick as 10 bagged and 3 loose (ready use).
10' high strength sewing thread.
1 ultrasound probe cover (unlubricated condom).
2 sheets rite-in-the-rain paper.
9 MP-1 tablets.
4' wire.
24 hooks of various sizes.
1 rubber jig lure.
20' 12kg fishing line.
36' of fly-fishing backing line.

I tend to have other things around me like:
Knife,
Multi-tool.
2-6 15' lengths of 550 cord.
E.D.C. ring.

Clothing as dictated by the weather. Mostly cold and wet.
Other tools and kit.

One thing that I do disagree about is the appropriateness of a fishing kit. Some people think that you don't need one. I don't completely agree with that.

Given that hooks can be used to catch birds etc as well as fish I tend towards the attitude that you should consider carefully before leaving them out. If you do carry them, carry a lot. Most effective methods of fishing (trot lines etc) require at least 5 hooks per set up. And you want to set 3 or 4 lines.