I exhaust all trading options, strategic bidding possibilities (I need 16th off so I make it the last day of availability and aggressive pickup something that ends late 15th or very early 16th), and then start looking at how fit I would be to fly if I was missing a family event. Certain bases are also willing to help because they know how difficult the company makes it but I haven't had to use that. I have had to bang out sick for doctors appointments which really screws up the schedulers but it is their system. You can also call up after a sick call and sit reserve another day to restore the sick time.