On your phone, build a cart out of five pieces of junk: a body (porta-potty, bathtub, grand piano, coffin, couch...), wheels, something to steer with, brakes, and one weird extra. The first build is free.
Everybody lines up side by side. When the countdown starts, mash PUSH: the more you mash, the better your start.
Put your thumb down and slide it to lean left or right. You're sitting up, so you're slower. Let go and you tuck: faster, but you can't steer. Hold BRAKE. Tap your EXTRA (a leaf blower, a bed spring, a pool noodle...).
Jumps with a gap after them (don't brake). Turns with no wall on the outside. A split down the middle. Oil, cones, barrels, a green tunnel. Fall off and a crane puts you back, slower and more broken.
Every heat pays by place, plus bonuses (longest air, no brakes). Between heats, buy better parts, tune-ups and repairs. Whatever breaks stays broken until you fix it.
The Mega Ramp. Double points. It falls apart behind you the whole way down. Fall off and the crane is slow; if the collapse catches you, you're out. Most points wins.
A lobby setting: the carts drive themselves and everybody just builds, watches, and honks.
Bodies: a porta-potty, a clawfoot bathtub, a shopping cart, a coffin, a canoe, an office chair, a grand piano, a fridge on its back, a cardboard box, a couch, a kiddie pool, a water heater.
Wheels: pizza cutters, roller skates, warble wheels off a shopping cart, bike wheels, tractor tires, four different sizes, donuts, office chair casters, red wagon wheels.
Steering: a rope, a doorknob, a dog on a leash, a bus steering wheel, a game controller, just leaning. Brakes: your feet, a stick in the spokes, an anchor, a parachute, a hand brake, no brakes.
Extras: a leaf blower, a bed spring, an umbrella, a bag of marbles, an air horn, a grappling hook, a pool noodle, a fire extinguisher.