water to cool off
If your school allowed it and you were able to do it at a profit, then yes you could.
You could try donating it to a school or possibly sell it on Ebay.
Roadrunner Sports does sell womens sports bras online from their website. They are really expensive though you could probably get the same thing cheaper from Walmart.
You can find numerous sites that sell positive promotions. There are sites that sell promotions that is relevant to what you need them for, for example: school, sports, jobs, and business.
marshmallows or doughnuts
There are companies that sell school signs to the public, but they need to first obtain permission from the school or else they could get into deep legal trouble.
How and where do you apply for a license to sell retail sports clothing?
You could try asking at a sports shop, if they don't sell them, they could probably give you an address of where you can. Failing that you could try ebay.
they could sell art, or other goods, or they could die.
Yes, they do sell camping accessories. They also sell a lot of other goods that have to do with being active. Sports Authority specializes in sports, but also most likely meet your camping needs.
to sell sports clothing and equipment, and make money.
You could sell an autographed field hockey stick from the 1964 Olympics through online auction sites like eBay or specialized sports memorabilia platforms such as SportsMemorabilia.com. Additionally, you could consider consignment shops that focus on sports collectibles or attend sports memorabilia conventions and trade shows to connect with collectors directly. Social media marketplaces and collector groups on platforms like Facebook could also be effective for reaching potential buyers.