If you have to transport the lemonade, you might like to make up a concentrate and mix it with fresh water on the spot, to cut down on the weight. To do that, mix 1 quart of lemon juice, 1 quart of strawberry juice or puree with 1 cup of sugar and 2 cups of light corn syrup. When you’re ready, combine the mix with 5 parts water (a little more than 3 gallons). Taste it, though, to get the right balance of tart and sweet.
If you'd rather not use corn syrup, you can make an adequate quantity of simple syrup and use that instead of the corn syrup and the single cup of sugar. (We always think it's nice to make sweeet cold drinks with a sugar syrup solution, because then you're sure all the sugar will be dissolved.)