Should I do this?

So I’m leaving this weekend, and will be leaving my 10 week old with family from Wednesday night to Friday night. He is breast fed and I have plenty of milk, but my question is about how to give it to my family. I have like 15 baggies of milk, but I don’t want to give them that as it may leak and just take up a lot of space. I was thinking of sanitizing a reusable water bottle and combining all of the milk in that. Would you do that? If not do you have any suggestions?