2015 Toyota Yaris manual transmission

[CrankyOldMan]

I agree that wheels and tires will give you the biggest boost, dollar for dollar. You're in FL, so you can run high performance summer tires pretty much year round. Anything in the 200-400 treadwear range will give phenomenal grip in the corners compared to stock all seasons and can be used for casual Autocross events.

It's tempting to go with the least expensive suspension first, but after looking at all the different stuff I've bought over the years, a decent set of coilovers would be cheaper in the long run. Plus you can dial it in exactly how you want it instead of trying to match two or three sets of springs to limited adjustment dampers.

Short shift kits under the hood are very hard to come by these days. TWM Performance still makes a short throw lever and bushings for the Yaris. I've actually got both an engine bay and a lever on mine and it's too short. I'd recommend the lever over the engine bay kit, but it's a little harder to install.

komichal's advice about a good set of automotive tools is also a solid investment if you intend to do anything else to the car in the future.