A souvenir kiosk at a venue is different from those at a mall. A mall kiosk is usually the one location for that vendor. In your case, a team store with a wider assortment of the same goods is within walking distance. Somehow, you've got to make your kiosk stand out.
Step one is making a visual statement. Honestly, if a kiosk looks like a watered down version of a full-blown team store, customers may not be motivated enough to buy, let alone pause to take a look. You need to make that kiosk look and feel special.
You can do it with one of the team's colors, showing all red or blue or black souvenirs. One big color statement is impactful. Fans won't be able to pass without looking. You can also use that kiosk to focus on a key demographic, such as kids. Or, the kiosk can specialize in a key category, such as headwear. Either way, the message to consumers is that your kiosk is special and thus is worth browsing.
Next is the location. Obviously, you don't want your souvenir kiosk to be anywhere near the team store. And where you put it can be based on what you sell. If the kiosk is kids' stuff, perhaps you set up near a dedicated family section, where kids run free. If the kiosk is hat-focused, try setting up near seating sections that company's rent out for events. These are people who don't frequent games and probably don't have a cap already. Bottom line? Think strategically about location.
The key to a kiosk, really, is the person manning it. Often, this goes one of two ways. For those of us who have been to malls, you know very well the hyper, pushy salesperson who openly solicits you to check out what he or she is selling. These are the people we avoid eye contact with.
We've also seen the oblivious mall kiosk salesperson whose head is always bowed over his or her cell phone. They couldn't care less if you stop to look at their selection of cell phone cases or jewelry. And as a matter fact, they'd prefer you just moved along so they can Snapchat uninterrupted.
An effective kiosk rep is one who makes eye contact with passersby and occasionally says hello without inviting people to take a look at the goods. Friendly, but not pushy. Sounds easy enough, but good luck finding people who can do it. To be fair, long hours of standing at attention can be draining. The pull of Twitter and Facebook and Pokemon Go can be too much to resist. A smart move might be limiting shifts to an hour, rotating employees from the team store to kiosk and back again.
The endgame is keeping your kiosk fresh and inviting. If put in the right spot, it can capture sales your team store missed.