Car washes actually do make a lot of money if you hold them outside a Walmart or Costco/Sam's Club while people do their shopping. And then you could also have a BBQ or something similar next to the carwash... You would need a lot of volunteers but usually the little girls like to wash the cars, with some older girl's help of course, and you can usually find a couple dads willing to do the grilling, and moms who like to bake. Do this for one whole weekend (Saturday, Sunday) and you could make a ton!
The leo sale is also a good idea, doesn't bring in a ton but most people can't resist it! You could sell them all for $10-$15 dollars, that's soooo much cheaper than they are new, and parents are usually willing to help because it helps them clear out their kids drawers. Also, I don't know how your gym does this, but mine used to do a team leo swap, because when they switched leos, compulsory girls got the previous optional ones. Sell these for $20 or so, since most aren't really that worn out from a couple meets a year. And you could sell the old track suits also, most little girls will snatch them up if if they're not the official ones any more.
The idea of a gala or show is great!