Just a lot of little stuff that comes to mind. I don't have any references to anything, just stuff I've picked up myself, been shown, or heard about.
1. Old blacksmithing trick: if your hammer head is sliding up off of the handle, flip the hammer upside down, choke your hand down a bit on the wood, and hold it with a loose grip. Smack the end of the handle, and the forces of inertia will push the hammer head back to the proper place. You should give yourself enough room on the handle, with the hand thats holding it, to 'catch' the handle from falling out of your hand after each blow. Then add a wedge to it.
2. No compass or map and it's too cloudy to see the sun? Pay attention to the folliage around you. If your in the northern hemisphere, moss will grow predominately on the side of a tree or rock that's out of the sunlight, creating a rough direction north. If your in an open plains and you know the predominate wind direction, check to see which way the grass is bent over. It's fairly common to see an entire field of knee high grass bent over towards the south east, if that's the predominate wind direction. Also, most trees and plants will grow the strongest towards sunlight. If you see a cluster of trees, where in one general direction, the branches on each tree are pretty short and/or little foliage on them, but on the sides and front of the three, the branches are really thick and stretch out away from the trunk, it can act as a rough guide north for you. Plants need sunlight, and they'll stretch for it and put most of their energy into reaching that direction, often leaving the backside rather sparse (ever notice how your christmas tree usually has a "bad side"
3. A blade of grass stretched taught between your thumbs can create an emergency whistle.
4. If your trying to siphon gas out of a car (with the owner's permission of course) check to see if there is any gas in the tank first, by blowing into the hose and listening for bubbles. Can save yourself some time and energy.
5. The amount of heat put out by firewood, is directly related to it's weight (when dry of course). Something to think about when falling timber on your property/buying firewood/whatever.
6. If you ever are faced with the situation of having downed powerlines in your path in a SHTF or whatever scenario. The wider the wires are mounted apart, the more distance they require to not arc into each other. Some of the large lines on the steel towers that carry power from one region to another can have up to 12-16 foot spaces between lines. Some of the powerlines you see on the urbam street only have a few feet between lines. Use this as a rough indicator of the proximity you can get to them. Obviously you should avoid downed powerlines at all costs. But realize that some lines can arc out and get you quite a bit further than others. If you made it passed one set, dont assume you have the method figured out, the next set of lines can be a lot bigger and meaner, and reach out quite a bit further.
7. If your in your vehicle on a very steep incline and your engine just died, but you still have battery power while driving a stick. You can use your starter to repeatedly lunge your vehicle forward by leaving the clutch out while turning the ignition. You run a high risk of burning out your starter doing this, but if it's a last ditch effort, it's a tool of knowledge that can make or break a situation. Can also be used to lunge a vehicle forward off railroad tracks if broken down, last couple yards to a gas pump, etc.
8. You can magnitise a tool (screwdriver for example) in a pinch, by wrapping a short length of wire around the metal and touching your vehicles battery terminals with each end. Wear gloves or something, so you dont get burnt. Only takes a fraction of a second, but if you need it, it's another option.
9. If you're building a fence, placing the fence posts in upside down, will make them last longer.
10. If you make a pot of coffee and you dont drink all of it and it gets cold, use it to water your plants. It has a high amount of nitrogen in it and your plants will be happy.