The great thing about teaching Kindergarten and Pre-K is that you can still have fun while learning. But one of the best things I ever did was to declare every Friday a "Fun, Fun Friday". And we would do an activity to celebrate making it through another week.
1. When studying letters and letter sounds, have the children do or bring something that relates to that letter. A stuffed animal for T - toy. Or wear crazy/mismatched socks for S. Or wear a shirt backwards for B.
2. Have them bring an item from home to share. You can either tie the article in with whatever you're studying (language arts, math, science, whatever). Or just have a plain ole Show and Tell day, the way we used to when we were in grade school.
3. Have a guest visitor no one expects. Again, you can tie it in to a study unit, or a holiday. (This can be as simple as having someone to come read to them.)
The possibilities are limitless! But by having Fridays special, my kids were less likely to miss school on those days!