The best thing to do is to get the Sterilized Alcohol Wipes.
These come in a box of like 100. Each is in a small, seled wrapper. Open it up, and you get a small cooton or cloth wipe, soaked in alcohol, and sterile.
They are available over the counter at pharmacies, even in states where needles are not sold OTC.
Just walk in, get a box.
These are the best. Use one to wipe off the tops of your vials before withdrawing (ahhhhhh ....... didnt think of that one - did ya?), and another for final cleansing/disinfecting of the injection site.
Smal, cheap, clean, neat, effective.
Much better than cotton balls, and a big bottle of alcohol.