This isn't outside or anything, but I thought it was a cute idea. Apparently, Pizza Hut is sponsoring fundraising things now where you have a group of your sisters come to eat at one of their restaurants and your organization gets a portion of the profits from the food. I got a flyer about it when we ordered a pizza couple of weeks ago. It was pretty cool and certainly seemed easy enough!
Also, I don't know what type of venues are in your area, but I know that in Atlanta a lot of groups make money by working as food or drink vendors during concerts, car races, etc. You could probably check with popular entertainment venues in your city about this. My brother's baseball team in high school was able to put lights up on the baseball field by working at the Georgia Dome a couple of times as servers during concerts and business functions (for example: Home Depot had a huge catered meeting that included entertainment by Jeff Foxworthy, a very popular Southern comedian. My brother worked with his teammates serving food that night and made tons of money, plus got to see Foxworthy perform for free!).
Good luck with whatever you decide to do!