Ever since my kiddo was little, we called Friday "La Vida Loca Day". It was used to give her something to look forward to when Saturday seemed like it was too far away. La Vida Loca Day starts as soon as school lets out. It's a day to leave the dishes in the sink because Saturday morning is our house cleaning time and leaving them overnight does no harm. I suspect that the cats like it, because they can jump on the counter and sniff around for leftover tidbits while their human slaves are asleep.
It's also the night when she's allowed to stay up as late as she wants--yes, she's 17 and still has a bedtime of 9:30 on school nights and always will until she graduates--but she usually goes to sleep earlier than on any other night. By the time Friday comes, she's pretty exhausted and in need of more rest. However, I think it just feels good for her to know that if she wanted to, she could stay up late.
It's not some ancient tradition or extravagant affair, but I do hope that she will have La Vida Loca Day with her kids.