Start with the simple stuff like 1) Pop Charger 2) Cat Back Exhaust 3) 3" Down Pipes (huge difference) 4) High Flow cats or Test Pipes (huge differece) 5) AVC-R helps build boost faster 6) Dual Pop if still have money
Then you get into the bigger engine stuff like
Larger Throttle Bodies Extruded honed and polished intake plenum Port Matched and Polished Lower Plenum