The coins/redemption desk would be the easiest way - people can use coins to purchase a coffee voucher. Then you organize separately with the coffee vendor to supply a free coffee to anyone who shows the voucher. You’d just work out with the coffee vendor beforehand a set limit to the total number of coffees, and how you’ll reimburse them.
You could do much the same thing by creating a badge called “Free Coffee”, which people show to your coffee vendor, as long as you’re not worried about people redeeming more than their fair share.
A redemption desk is probably the best option for a big public type of event so you can offer great prizes/incentives and control them more – this is something you can on-sell to prospective exhibitors and also ask them to donate a prize (e.g. something of fairly low wholesale value to them but high retail value).
But if you really don’t want a redemption desk, and you want to make sure each attendee only claimed one coffee (or whatever the item is), you could do the following. We’re using coffee as an example, but more likely you’d do this for a more expensive item being earned less frequently.
Create a hidden goal called “Redeem a Coffee” with no points. Then either:
Give the coffee vendor a slimmed-down version of the Organizer App, so they could see if a person had already redeemed their coffee.
OR
Have the attendee show the coffee vendor their badge, and give the coffee vendor a QR code on a laminated card that they keep behind the counter. Anyone who shows the badge can scan the code. The ‘goal’ is achieved. By setting a personal inventory of 1, you can ensure attendees only redeem once, and you could also limit the total goal inventory for the event.