What are the best upgrades/modifications that I can make to my vehicle for <$100?

What are the best upgrades/modifications that I can make to my vehicle for

reducing weight is free

Depends entirely on the vehicle and how handy you are with a wrench.

Mud flaps

Reducing weight is extremely expensive. Carbon fiber/aluminum/fiberglass/titanium bills run high quickly.
Removing parts is usually free, but can sometimes cost a fair amount for proper deletes.

Full tank of fuel.

Removing shit from the car is free, real weight reduction like what Motorsports teams do is notoriously expensive.

A tank or two of petrol and/or a track day.

The easiest and cheapest way to make your car faster is to improve the driver

Have a tiny Mexican man clean the shit out of your car.

Phone mount.

Springy antenna.

Spark plugs and coil packs, injector clean.

Brake pads.

25 Black Ice air fresheners.

Upper strut bar(s)

Nice one. Don't buy a shitty strut bar though.

New oil filter and fully synth oil, air filter, spark plugs and if your car has also ignition leads and injector cleaner/fuel system cleaner additive.

New badges
New headlights
Tow hook
New tail lights
200$ for window tint

Cold air intake
Screw on exhaust

found the ricer

>Cold air intake

Mate are you retarded

Stickers add +5 hp. +10 if they are red

Still infinitely more than a cold air intake

Front/Rear sway bars can be pretty cheap and have a good effect on handling in some cars.

Strut tower brace

A good wash, flowers, and motor oil. If your car loves you it will run better.

flaps

A Turbonator™ in the intake.

GENERAL MOTHERFUCKING MAINTENANCE
Unless you've caught up on it... In that case save for next week when the next thing breaks because you're poor(it's ok I'm poor too) Oh buy some Black Ice® too

>basic maintenance
>clean your car
>fill that bitch up

You know you buy a really cheap car when a full tank is the convincing argument to actually buy it.

Windshield water repellent.

Why not?

Rip out everything that isn't too stubbornly bolted down or absolutely necessary for basic operation, perform whatever maintenance you have been neglecting, and spend the rest on stickers. $100 really doesn't go far in the automotive world.