Depends. Is your club at a fairly popular barn? Here's a few things my club used to do:
1. Tack cleaning - Advertise at EVERY barn in the area, and even in the paper if possible. You can ask for donations (cleaning supplies, money) or you can charge per item, like $2/bridle, $5/english saddle, $10/western saddle. Use the all-in-one cleaner so you make more money.
2. Horse grooming - "deep clean" a horse. $5. Mane pulling or extra dirty horses $10
3. Auction - Tack and people, or just people. Set a price that a person will work for an hour, like $10. They can help clean barns, mow, fix fence, etc. Basically help the "buyer" out with whatever needs done.
4. Candle fundraiser. We found a company that sold candles and other smell-goods and did just a plain ol' fundraiser, order forms and all.
5. Trailer/truck cleanout. Obviously depends on the weather, but basically its the 8th grade car wash, in horse people terms. Wash outside of both vehicles, $15 cleaning inside horse trailer $5 extra or something.
6. Do a Kid's Kamp. Pick a Saturday late morning or early afternoon at your club's stable, get the more laid back horses, the knowledgeable riders, and do pony rides, games, basically "this is a horse farm!" type stuff. The stable should have safety waivers for every rider at the farm. Charge like, $5/kid.
I don't know where you are in the Midwest, but Kroger's (grocery) has a great fundraiser that you don't have to do much to set up - just buy groceries. Get your relatives and friends to buy groceries etc etc and it all adds up.
If you have Kroger stores - check out their web site for community rewards.
Shot glasses with suggestive equestrian themed sayings ("get lucky", with a horse shoe on it), "save a horse" with a bucking horse/cowboy on the other side.
Rubber bracelets (a la Livestrong) in your schools colors with your schools motto and or mascot word/name on it. We mixed and matched the combos, and sold them for a slight discount if they bought 2 or more. Since they're not all the same, people didn't mind.
One of the clubs here paints old horseshoes in the school colors and cute designs with our school name and sayings....sell them for about $2-5... you'd be surprised at how much they actually make- even non horse ppl like a good luck horseshoe! And they got the shoes from the farrier for free.
Ask around at local restaurants. A lot of them will let you go work there for a night and get a percentage of the proceeds. A lot of ice cream shops and pizza places are good for this.
Our polo club used to direct parking traffic on one of the golf courses for football games for a fundraiser. The school would pay the club $X/hr per person. We did every home football game. It usually worked out to each member had to do 2 or 3 games and it was usually a few hours commitment. We brought our goat mascot and generally had a good time with it. See if your school does something like that.
Bake sale set up in the Student Union or some other high traffic area.
I don't know if this would fly now with all the vendor fees...
but we went to A shows in the area and worked. We had four people who could do A quality braids- so we put flyers up for that. Then, we set up a little pop-up tent and offered tack cleaning, boot polishing, resewing lost buttons, and anything else we could think of. We also brought out equestrian team hats and sweatshirts to sell.
Offer free pony rides at your horseshows but charge for concessions (and provide good ones that people want to buy). Advertise the pony rides well and they will draw families out to the show, which means they'll be likely to pay for concessions.
College students will always buy a well-designed fun unique t-shirt, period. Our riding team t-shirts sold out every year and were always popular with non-horsey students for sure - they were sort of "collectors items."
Love the horseshoes painted in school colors - that is a terrific idea!
I'd market any fundraising idea to the general non-horsey population while appealing to good old school spirit, actually.
While selling grooming/braiding/barnwork and putting the profits toward charity might sound like a natural fit, remember that you'll be "competing" against the professionals who actually get paid to do the same work full-time. Might not be very successful.