I must agree that fish traps, gill net and trot lines are probably the most effective "passive" methods of collecting fish. However, most are illegal outside of a real survival situation which sucks because you can't practice. Most states allow trot lines...with something like 25 hooks being the maximum...that's still pretty big for one or two people.
I just updated and made a few more small kits. I just like using them when we go backpacking and most of my fishing in the last couple years has been my short packing pole (Emmrod) or improvised from my "survival" fishing kits.
Here's a mini-fishing kit I have in my son's pack (bottom right corner). It works and he's caught small perch/sun fish with it in smaller pools long the creeks we hike:
Here's my old one...in a container a little larger than a film canister:
Here's my packing pole and another hand-casting device (can't remember where I picked it up) and my larger kit:
I just made a another hand caster with a small plastic tube...works quite well. Dave Canterbury of Wilderness Outfitters Archery does several decent You-Tube videos and a search of his stuff I found a great video he did on a hand-casting tube/kit. Pretty cool little kit.
Usually what I put in my kits (fresh water) are:
Assorted lead weights
Assorted hook sizes
Smaller treble hooks
Stainless steel leaders
Swivel clips (helps make a trot line)
Poppers for panfish
Dry flies
Artificial worm lures/hooks
A couple of jigs/spoons
Spyderwire fishing line (40-60 pound test)...excellent stuff!
I've used the small stainless sewing spools for the small kits. I can get about 40-45 feet on a single spool.
With a few safety pins, you can improvise a small fishing pole. I've seen one guy just carry a decent fishing reel and some zip ties. He finds a nice long sapling and trims into a pole. A few eyes for the line and zip-ties secure the reel to the pole. Much more compact than most set ups!
The kit I just built has those mini bobbers in them and some other different lures I want to try out. I'll need to get a picture up of the two larger kits.
I also added some small pouches of artificial bate (smells like dead fish:barf

, but I've heard it works great around here...anything to tip the balance.
In my larger "game kit", I have several of the yo-yo automatic fishing reels along with some of the Speedhook "fishing snares". Again, not legal in most states, but I can tell you they work quite well!
ROCK6