Jack, can I trouble you to keep an eye on my luggage?I need to go to the washroom.
杰克,能麻烦你帮我看下包吗?我要去趟厕所。
Will you keep your eye on my suitcase while I go to get the tickets? 
我去买车票时帮我照看一下手提箱好吗?
类似的表达也可以是
Please keep an eye on my bag while I go to the bathroom.
Please watch my bag while I go to the bathroom.
Please keep my bag safe while I go to the bathroom.
Please take care of my bag while I go to the bathroom.