if you bring powder you can make a bottle anywhere - any room, anywhere in the parks - it's very very easy.
We brought a travel kettle to boil water, but I understand that not all american moms use boiled water.
Either way, fill your bottle with teh appropriate amount of water, and then either measure your formula in to a suitable container (there is one sold especially for the job but anything would work) or even easier, buy the formula that is sold in pre-measured sachets.
Just carry bottles and powder seperately - no need to refridgerate as it's only water, and when baby wants a bottle you can just pour the powder intothe water, shake it up, and hey presto instant bottle.
If you need warm bottles then put hot water in the bottles and keep them in a seperate cool bag, which will have the opposite effect and insulate them, so the water will stay warm for most of the day