In a truly dire situation and speed is the key you may not have time to adequately sterilize your equipment, so first rule is to keep these things clean and in a airtight sterilized container, and definitely in the sterile package until they need to be used.
Unless the instruments are coming from a sterile unbroken package, you must sterilize them prior to use.
If the wound doesnt kill them the infection will. One of the main causes of death in prior centuries was not from injuries themselves but from unclean equipment, often you would hear that a patient had been operated on but a fever had developed and died days later, this is often an infection.
The best way to sterilize is with heat, High heat will kill almost all harmful germs, and wet heat from steam is always more effective than dry heat from an oven.
A simple rule is to sterilize all equipment before an operation and all instruments after that have touched blood or fluids.
Open pot boiling water requires 30 minutes to become sterile, but a closed pot with a cover to trap steam acts faster. However you must remember that water can rust metal instruments.
To prevent rust add 5 spoonfuls of oil to every liter of water you boil, then lay the hot instruments on a dry, clean (sterile if possible) cloth, this way the water can evaporate. NEVER PUT A INSTRUMENT AWAY WHEN IT IS STILL WET!
Sterlizing with steam under pressure is the fastest and surest method, and can kill harmful germs in 15 minutes. You will need a strong pot with a tight fitting lid.
The MSR stowaway pot would work well, but with any pot you will need to make a small hole for the steam to escape.
What works the best is a pressure cooker, as it has a s built in safety valve that releases excess steam.
For Pressure Cooker (or improvised) use
1) Put 2 cups of water and oil (5 spoonfuls per liter) in pot
2) Place the handles together. Put on high heat until a loud hissing noise begins
3) Put on lower heat. Begin timing now. Leave hissing pot on the low flame for 15 minutes. DO NOT LET THE COOKER BOIL DRY!
4) Cool the pot under water, open, and lay the instruments on a clean towel to dry
(Next time you use the pot, you can use the same water that was left inside the pot)
Sterilizing with heat is not necessary for instruments that do not touch blood. Say if you are examining a tooth, or rash, you can just clean your instruments and soak them in a solution of alcohol or bleach.
1) Mix in a large container every week
7 parts alcohol (95%) with 3 parts water and keep the container tightly covered to prevent evaporation.
2) Keep covered pan half filled with this mixture you will have to add some more of the mixture from teh large container to the pan every day.
3) Leave your instruments in the pan, completely covered in the liquid for 30 minutes.
Find cheapest brand name for bleach.
Make 1 liter of solution with a mixture of 1/2 cup bleach and 3 1/2 cups of clean water.
Bleach does rust metal instruments, so if they are not stainless steel add 1 large spoonful of baking soda (sodium bicarbonate) to the solution and leave instruments in for no more than 30 minutes.
Then wipe each instrument with alcohol to remove film of bleach. THen store it try inside a clean cloth or sterilized covered pan.
For disposable needles if you really have to reuse them, replace the cap very carefully and put the needle in pan full or bleach solution until you are read to clean and sterilize it.
Re-usable needles can be used over and over again, and this section is more geared towards them, but the same steps can be used (roughly) for non-reusable
1) put on a pair of heavy gloves to protect your hands from germs and getting stuck with the needle.
2) draw 5% bleach solution (see above) up through the needle into the syringe barrel.
3) squirt out bleach solution
4) repeat several times and rinse everything several times with clean water (you dont want bleach residue in the needle to go into the patient, it can be dangerous)
5) Take the syringe and needle apart and boil or steam them.
This should go without saying but NEVER REUSE A NEEDLE UNLESS YOU HAVE STERILIZED IT!!!