Since tomorrow is the last day before vacation and the kids might be slightly wacko and unwilling to work, make sure you work them anyway, or give a test. There is bound to be an administrator lurking around with a computer, just itching to do an observation. The day before a holiday is their favorite time. And, the later in the day your class meets, the better your chances are of getting this unexpected visit.
Admins don't think there is any problem with doing this. One said he liked to observe this time to see what stuff teachers are really made of. I said, if he doesn't know he is not much of an administrator.
Have a great vacation and good luck tomorrow. I know from experience it will be rough.