The Patty Wagon is a vehicle that is shaped like a Krabby Patty, and it is shown to be built with layers of ingredients like a real Krabby Patty. It is said by SpongeBob that Mr. Krabs uses it for promotional reasons.
The Patty Wagon appears in The SpongeBob SquarePants Movie, where SpongeBob and Patrick ride it to Shell City. It is stolen as they cross the county line. However, it is then brought to the Thug Tug (a rough biker bar), in which SpongeBob and Patrick are able to get it back. They then ride it through the abyss. After they land on the road after a jump while dodging the fake ice-cream vendor, they are separated from the Patty Wagon, which is then eaten by a frogfish and then by a larger fish. It is presumed to be lost and destroyed.
Outside of the movie, the vehicle appears in The SpongeBob SquarePants Movie Video Game in the driving levels "Sandwich Driving 101," "No Weenie Parking Anytime," "Sundae Driving," and "Drive of the Knucklehead McSpazatron." Despite having been eaten by Frogfish in the movie, Mindy is able to retrieve it for SpongeBob and Patrick prior to the start of the "Drive of the Knucklehead McSpazatron" level if the former gives her fifty Goofy Goober tokens. If the player causes damage to the Patty Wagon too many times, it will break down by its ingredients dissolving, thus restarting the level.
Almost every part of the car is designed to be food or food-related. The car has:
Sesame seed surface finish.
Grilled leather interior
Radial pickles (also called "Steel-belted")
Fuel-injected deep fryer with dual overhead grease traps
According to SpongeBob, he doesn't need a license to drive it.
The ingredients on the Patty Wagon are not connected to each other (seen when SpongeBob and Patrick bashed the Wall of the KK2 and the ingredients/parts fall down to each other). It is unknown how the PW works.
It was revealed that the patty wagon has a manual transmission. SpongeBob is seen making an "S" like shifting maneuver, seemingly shifting from reverse to first. Also, while SpongeBob's driving away from the Thug Tug, we can see a 3rd pedal, most likely a clutch. Both these features are exclusive to manuals.
Also, the fact that it runs on fry oil probably means it's a diesel engine set-up. Likewise, diesel fuel isn't volatile enough to burn in a spark-ignition gasoline engine.
This is a particularly interesting joke on SpongeBob's driving skills; as he is able to drive a vehicle (that's not a boat) with a manual transmission (which takes significantly more coordination to drive) on city and country roads, while failing miserably driving an (presumably) automatic on a closed course.
It is likely all KK employees know the shift pattern by heart (there is roughly a dozen types of shift patterns on manual transmissions) as SpongeBob was able to (presumably) shift effortlessly, despite there being a customized shift knob. Patrick probably watched SpongeBob shift (enough to know where reverse and first gear are), as he was seen backing up and driving forward to save SpongeBob.
Northern Leisure Group made the ride out of the Patty Wagon featuring SpongeBob and Gary. The ride features sing-a-long lyrics in time with the theme tune and horn, bubble and dolphin sound effect buttons.