So I'm leaving my baby with grandma for 5 days while I go out of town and haven't been able to save up enough breastmilk…

So I'm leaving my baby with grandma for 5 days while I go out of town and haven't been able to save up enough breastmilk in my stash for him.. not sure what to do. Leaving tomorrow so a donor is pretty much out of the question. He's never had formula before and I'm afraid of him having a bad reaction to it especially if I'm not going to be there. He's 9 months old by the way. Help please! 😩