大多数不需要：

winter break:I'm going skiing during winter break.我放寒假期间去滑雪.

Christmas:It's snowing on Christmas day.圣诞节那天在下雪.

weekend:What are you doing next weekend 你下周末打算干什么

school day 前面也不需要：I can't play computer games on school days.我上学时不能打电子游戏.

但是,若是强调某一天时,可以加上冠词：

It's a school day tomorrow,I can't stay up too late.明天我还要上学,所以不能睡得太晚.

But it'll be the weekend,sure you can have some fun.可是那是在周末,你难道就不能放松一下吗

前面应该加定冠词the

看在哪种情况下

通常要的a school day