Once DS hit one (actually at 11.5 months) , I cut the mid-day formula feed out and just left it at a morning and night bottle of formula. I think that's pretty normal at 1yo as solids become their main source of food and not formula/milk, so 2x8oz bottles is enough milk for them. I started it at first by not taking a bottle for him when we were going to be out in the day, and he was usually so distracted by whatever was going on that he didn't notice. Days at home I cut the feed down gradually and once he was only taking 2-3ounces just stopped offering it.
So not really an answer to the storage question, but this way there is no need to worry about it, kwim? Otherwise, I'd just go for an ice pack in a cooler box. HTH.