(Wraps arms around neck and uses G4 + G3) "Gomu Gumo no Suffocation!" Imagine Gear 4 arms choking you? Goodnight. (This got darker than I thought it would, oi).
Use bladed weapons. I actually have a theory that Luffy could use a sword at the end of the series, since Roger (whose Will he inherited), and Shanks, his mentor, also use one sword. I wouldn't be surprised if Luffy fights with a sword by the end of the series, but, right now, he's not willing to kill enemies in combat. Luffy has never tried to kill anyone in the main series, as far as I know.