包括元旦在内我有三天假期用英语怎么说

You can say "I have three days off, including New Year's Day."

"Days off" is a common expression to refer to time off from work or school. "Including" is used to specify that a particular item is included in a list or total.

Here are some examples in English:

I'm taking a three-day weekend, including Monday.
I have three days off, starting from tomorrow.
I'm planning to use my three days off to travel.

In Chinese:

我有三天假期，包括星期一。
我从明天开始有三天假期。
我打算利用这三天假期去旅行。