I stopped buying the cookies 20 years ago.
The cookies are good, but they're waaaaaay too expensive, an very little goes to actually fund Girl Scout activiities. For whatever reason, the Boy Scouts seem to do a better job of providing for the kids. IMHO, GSA is more about raising funds to support the GSA corporate bureaucracy by exploiting child labor to sell cookies.
BTW, I don't flatly refuse to donate. I just don't buy the cookies. Whenever I'm approaced by somebody wanting to sell cookies to me, I make a $5 or $10 cash donation instead. The local troop gets full benefit from my donation without having to fork over 99% to the national GSA and cookie manufacturers.
When you buy any product from a Boy Scout, none of it goes to the BSA's National Council. If you buy the popcorn, approximately 1/3 goes to the manufacturer of the popcorn, 1/3 to the Pack or Troop the Scout belongs to, and 1/3 to the local Council.
The local Council uses it to pay their staff (both full time and seasonal summer camp), maintain their properties (repair the dining hall, etc.), and purchase program materials (new canoes for summer camp, etc.). If you'd like to see a breakdown of how the money works in your local Council, call them up and ask for a copy of their Annual Report.
The Troop or Pack will use their money to buy camping equipment or other program materials. This can get expensive. The tents we buy for our unit cost about $240 each for two young men to use. Sure, we could buy the $89 special from Wal-Mart, but then what happens when you have a thunderstorm? It collapses, the kids get soaked, and they'll never come out on a campout again. Unlike GSUSA units, BSA Troops have to go camping, it's part of the program. A good Troop goes camping at least 9 weekends in the year, plus a week of summer camp. So they all have their own gear. GSUSA units generally don't camp all that much (they can if they want to, but the program doesn't require it), so they usually have no need to invest in the equipment. The local GSUSA Council thus stocks the equipment needed.
By the way, other fundraisers that a BSA unit runs, like a Troop selling Christmas trees, don't include the local Council. For example, we sell wreaths. Half the money goes to the manufacturer. Of the other half, half of that goes to the Troop's general funds, and the other half (1/4 of the price) goes to the Scout's "Scout Account". We keep this money separate on the unit's books, and the Scout can use it for uniforming, camp fees, camping equipment, hiking boots, etc.