You can get plastic disposable pastry bags at like Michael's and Hobby Lobby. You can use those for the dry bags. They are cone shaped so they look nice and they are cheaper and easier to transport than jars. Tie the top off with pretty ribbon and voila!
I would get a scoop that you can use for cookie dough. This makes it easier, faster and less messy for you plus more of a uniform shape for the customers.
I'd say basic cookies like choc. chip, M&M, peanut butter are for sure plus brownies and other breads. If you can make from scratch I'd do it...I can always tell mix products, but if it's for charity even I would look over that fact! ;)
added: I was thinking that you can make your own chocolate suckers/candies for pretty cheap and they are so easy! If you get a chocolate mold at a cake shop (or craft store) and buy the already tempered chocolate discs...melt them, pour them in the mold, put in a stick, freeze for 5 minutes and done. They are easy and look cool and would probably be a good seller!
Also you may want to consider doing 1/2 dozens...just a thought but if you pack everything in groups of 6 you'll probably sell more and you can still offer a price break for a dozen, just give them two bags of 6.