Transition to whole milk

Hey moms ! So my 13 month old is now transitioning to whole milk. She was breast fed the first 4 months of life then she was formula fed. Now that she is taking whole milk I was wondering how do I pack her bag as I run errands with her. Normally I would have the formula dispenser with water already in the bottles. So now I’m wondering am I going to have to keep the whole milk bottles in a bag cooler as were out ? Seems like a lot of work. I’m a FTM so Idk what most moms would do at this point. She is eating more and more solids but she still wants /needs her bottle. Any suggestions?