Not very many N64 games received pre-release demo versions. The few that did exist came in carts meant for kiosks only, with instructions that the cart was meant to be destroyed by the store manager upon release of the actual game. Luckily, a lot of managers didn’t listen.
These demos are the most valuable carts in the entire N64 library (except for Sculptor’s Cut) because they contain beta material not present in their game’s final ROMs. The Donkey Kong cart pictured here contained two boss fights and a mine cart ride, but hackers managed to find much more inside (not in terms of entire levels, but in abandoned models). It also contains an alternate opening with more chimp screeches and a lengthier session of acrobatics by the “N” logo.
Demo carts for Majora’s Mask and Turok 2 also exist (more on those whenever they appear). If you can afford them, they’re cool slices of game history to have. In addition, a Pokemon Snap demo cart was created for the Blockbuster Snap Stations, but contains no beta material (it just ends early and that’s all that’s different).