As to the sterile part... swab off the top with an alcohol sponge (they come in boxes of about 100) and you should be ok there.

The temps I never thought about. Never seemed to bother mine and I've kept it in the truck so....

Also you might want to keep a can of Red Bull handy in case of emergency. Chug it at the first sign of a hit and a lot of the time it will abort the hit. 

Proper "sterile" injection technique from liquid vials (in your case, sumatriptan of course):

1.  Swab the top of the vial with one alcohol pad and let dry, then swab your injection site* and let dry.
2.  Get your needle ready and draw in some air -- if you're injecting 3mL, draw up 3mL of air.
3.  Inject air into the vial.  (This breaks the suction, making it easier to draw up the meds.)
4.  Now draw up the correct amount of med.
5.  Inject in your already-swabbed spot!  Acceptable spots listed below.  Also, it's important to note that you may receive needles that are longer than a typical subcutaneous injection should go.  It's NOT necessary to insert the needle all the way.  I was so gung-ho when I started that most of my shots were ending up in the muscles--too deep.

*Acceptable subQ injection sites:

Upper Arm: Uncover the arm to the shoulder to see the whole arm. Have the person getting the shot stand with hand on hip. Stand next to and a little behind the person. Find the area in the middle part of the arm, halfway between the elbow and shoulder. Gently grasp the skin at the back of the arm between your thumb and first 2 fingers. You should have 1-2 inches of skin.

Abdomen: Uncover the abdomen to see the whole area. Find the waist area. You may give a shot bounded by these landmarks: below the waist, to just above the hip bone, and from where the body curves at the side to about 2 inches from the middle of the abdomen. Avoid the bellybutton. Use the natural line in the middle of the body as a marker. It may be hard to see, but it is there unless it was removed by surgery.

Thigh: Uncover the entire leg. Find the area between the knee and hip. The middle of the thigh, from mid-front to mid-side, on the outside part of the thigh is a safe site. Gently grasp the area to make sure you can pinch one to two inches of skin.

Lower back: Uncover the back from the waist to the top of the rear-end. A shot may be given just below the waist to a line that runs across the back above the crack between rear end cheeks. Give the shot between the area where the body curves at the hip and a few inches from the spine.
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All of that being said, when the beast comes calling I just grab the nearest syringe and let fly!  Sterile technique goes right out the window.   

Just fill two syringes and cap one for later