Welcome........ Do you have a Coupe or 4 door?
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@Nix said not much in the way of performance mods, but a healthier sound can be accomplished. As for better gas mileage, I'm the man

....... My record is 48.9 mpg, just think how many ppl would be complaining if I had the job of testing mileage for Honda.......
1st thing is to have your tyres inflated according to the door sticker, take it out of traction control, learn to use the cruise control appropriately for achieving better mileage(can get into how if interested?).
I was getting my 48.9 doing a ride at speeds from 60 to 70 mph, and was going from a lower to higher altitude.
As for local driving, looking as far down the road as possible so you can keep as steady a pace as possible, without having to brake or accelerate will work the best, drive-through fast food places will kill it.
Also using your shifter can do a lot for performance. Knowing what each gear does helps as well..... 1st is 1st only.......2nd is 2nd only....3rd is 1st thru 3rd......Drive is 1st thru 2,3,4, &5.......
I've replaced the chicken wire for a rear sway bar, 22mm thick, very good improvement($200+ from "Progress").