Would it be better for me to take a leave of absence if I'll be gone for 3-4 weeks or just take off all the weeks (assuming my manager approves it)

I work at Starbucks part time, mostly for fun and to get away from academia. I'm a graduate student and I just found out my lab is planning field work during Thanksgiving break, and also the week between Christmas and new years. To further this, I'm helping to co-teach a class for two weeks abroad so I will also be gone for that.

What's my best course of action? I'm planning on letting my manager know on Friday when I see him.