This guide aims to list each part you can add to your car along with any relevant info about the part and how it affects your car.
All the stats are taken from the game items.

The engine is an essential part of the car and determines how fast your car can go. They can be found in an abandoned car, a scrap yard, or bought from a Laika dealership.
I'm pretty sure some stats are wrong (for example some of the squash engines acceleration stats don't seem to make much sense) but I wrote them as they appear in the game.

The fuel tank is an essential part of the car and determines how much fuel your car can carry. They can be found in an abandoned car, a scrap yard, or bought from a Laika dealership.

The carburettor is an essential part of the car and determines the fuel efficiency of your car. They can be found in an abandoned car, a scrap yard, or bought from a Laika dealership.

The air filter is a non-essential part of the car and protects the engine from a percentage of damage. They can be found in an abandoned car, a scrap yard, or bought from a Laika dealership.

The ignition coil is an essential part of the car and determines how fast your car starts up and the fuel cost for starting it. They can be found in an abandoned car, a scrap yard, or bought from a Laika dealership.

The battery is an essential part of the car and powers all electrical components, including the ignition, headlights, interior light, radio, and windshield wipers. They can be found in an abandoned car, a scrap yard, or bought from a Laika dealership. All batteries are statistically identical with a cost of 10, durability of 3, and a weight of 1kg.

The water tank is a non-essential part of the car that provides water to the windshield wipers. They can be found in an abandoned car, a scrap yard, or bought from a Laika dealership. Note that the water you add to the water tank gives it more weight, e.g. empty gazelle water tank: 2kg, full oasis water tank: 3 kg.

Tyres are an essential part of the car. There are currently three kinds of tyre, the Road Tyre gives increased traction on dry roads, the Wet Tyre gives increased traction on wet roads, and the Off-Road Tyre gives increased traction on dry off-road trails. All of them have a duribility of 3. When broken they will no longer provide any traction and it requires a Car Jack to replace or repair broken tyres. They can be found on abandoned cars, in scrap yards, and bought from petrol stations and outershops.

The mud guards is an upgrade that passively reduces the amount of mud that acumulates on your car. they are placed near the wheels and once attached cannot be removed. Like all upgrades, they do not require repairs or cleaning. They can be bought from Laika dealerships and have a cost of 25.

The bull bar is an upgrade that passivily reduces the amount of damage taken from crashes. It is placed on the frount of your car and once attached cannot be removed. Like all upgrades, it does not require repairs or cleaning. It can be bought from Laika dealerships and has a cost of 100.

The light rack is an upgrade that adds extra headlights to the frount of the car, allowing for extra visibility. It is placed on the frount of your car and once attached cannot be removed. Like all upgrades, it does not require repairs or cleaning, however they do use a small amount of electricity while active. It can be bought from Laika dealerships and has a cost of 200.

The digital dash is an upgrade that displays when a part is damaged, when your low on fuel or water, or if you are carrying to much weight. It is placed behind the steering wheel and once attached cannot be removed. Like all upgrades, it does not require repairs or cleaning. It can be bought from Laika dealerships and has a cost of 400.

The roof rack is an upgrade that doubles the amount of storage space you have. It is placed on top of the car and once attached cannot be removed. Like all upgrades, it does not require repairs or cleaning. It can be bought from Laika dealerships and has a cost of 300.

The tool rack is an upgrade that stores tools, it comes with its own car jack, crowbar, and unlimited use wrench. There are three levels of tool rack that must be bought sequentially, lvl 1 comes with a bronze wrench that can repair parts to 33% durabiliy, lvl 2 comes with a silver wrench that can repair to 66%, and lvl 3 comes with a gold wrench that can repair to 100%. It is placed in the trunk and once attached cannot be removed. Like all upgrades, it does not require repairs or cleaning. It can be bought from Laika dealerships, lvl 1 has a cost of 300, lvl 2 has a cost of 400, and lvl 3 has a cost of 500.

The passenger side door replacement makes the handle not jam.

Paint allows you to recolour your car. Colours will graudally increase in opacity as you paint, allowing you to mix colours. Spraypaint cans will eventually run out of paint so it is not advised to spray anything that isnt your car. Various colours can be bought from Laika dealerships, regular paint has a cost of 20, metallic paint has a cost of 40.

Decals allow you to add various patterns to your car. Decals will overlap so colours cannot be mixed. Decals come in a box when bought and disappear when used. Decals can be removed using a decal remover, which can be found at home or bought from a Laika dealership. Various patterns and colours can be bought from a Laika dealership and have a cost of 40.

Feel free to point out any mistakes or missing info in the comments and I'll try to fix it asap. :P