I have been to a couple of events that give prizes for the person who
came from the furtherest distance to the gathering (I get that one a
lot when I go to East Coast gatherings :-)

Or the Person who has the most Plants, and the Person who has the
most Finds. (Log books must be present to confirm these claims)

The Person who found the most letterboxes on the day of the gathering!

The Person who has the most exchanges in their logbook (or the person
who has been to the most gatherings)

Prizes can be as simple or complex as you choose them to be. I have
seen Certificates made for the Most Plants, Most Finds. I have seen
Ink Pads or Rubbermaid containers given away as prizes. Especially,
fancy ink pads like Dabbers or ink pen sets.

Carving Kits are another good prize, especially if you give a prize
to the most Newbie letterboxer to attend your gathering! We were at a
gathering once when a person showed up who had never been
letterboxing (no plants and no finds until that day), and they showed
up to see what the deal was...

-Amanda from Seattle