If you don't have a tonneau cover, then it's worth it to get one. It will help the aerodynamics which will help gas mileage and it will keep the bed clean and dry. What size truck do you have?

Its a nissan frontier King cab...its about the size of an S10 I guess.

CAI will decrease gas milage. If you want a power increase (burn more fuel) get a CAI otherwise get it as hot as possible. Running the hot air all the time until like 80% throttle would be ideal.