Being a HMB local (and RV-7 builder) all of the above are great suggestions. Park at the south ramp; you have easy access to some great food (Mezza Luna italian, Old Princeton Landing (bar/burgers), Half Moon Bay Brewing Co, Barbaras fish trap (best fish and chips around) ... lots of others, too!) It's an easy walk to the bluffs by the airport and to the ocean. It is pumpkin season and HMB is the a self-proclaimed Pumpkin Capital, so bring a few home. There's a farm/pumpkin stand right across from the terminal building. Downtown HMB is quite charming, but it's about 4 miles south, so it would be a bit hard to get to. Watch the WX; we enjoy the famous SF fog, so it may be able to get close but not all the way in w/o an IFR ticket, however, as fall encroaches, the fog leaves and the WX is generally good for VFR.
Feel free to PM me with any questions; I'll be happy to help you enjoy our coastal town.