With 9-14 feedings a day, I'm not sure this would be economical but it would be the most convenient. You didn't mention how many ounces your daughter drinks per feeding. There are ready to feed formulas that don't require and powder, water or measuring. You just open the can (8 oz or so) and pour it in the bottle or in some cases open the bottle put a nipple on it and it is ready to go. There are also cans with about 32 oz of ready to feed. You can pour it out in 8 (or so) bottles with the ready to feed before you go to the park and then store it in a cooler and pull out a bottle as you need it. If you must use powder, if you have enough bottles to last the day, I would measure out the powder before you head out in the morning and bring a liter or two of water with you and as you need the formula, just fill the bottles with water and shake it to mix it. Just make sure no one drinks for the bottle of water, you don't want bacteria getting into the water. If you only want to bring a few bottles with you then you'll have to wash the bottles, bring the powder and water, measure and mix as you go.