The coastal area of San Mateo County has a lot of interesting areas for cycling. If you don't mind riding a paved shoulder while traffic zooms by, Highway 1 is bikeable along most of its length through the county. There are also many scenic side roads through rural areas.
Most cyclists probably arrive by car, or bike in from elsewhere. If you are cycling alone, you can also get to the area by SamTrans bus to Half Moon Bay or Pescadero. You can also take Santa Cruz Metro bus 40 to Waddell Creek. However, since the bike capacity is limited on buses, groups are out of the question. If you are arriving from the north, Highway 1 through the Devil's Slide area (between Pacifica and Montara) is very bike-unfriendly; use the old road (now a fire road) that goes across Mt. Montara.
Hostels are at Pigeon Point and Point Montara lighthouses. Since these are popular (especially when it is warm), a reservation is usually necessary. If the web sites say that they are full, then try phoning: they seem to keep a few bunks unlisted on the web reservation system.
The Half Moon Bay area has all kinds of places to eat, from fast food to fancy restaurants, and supermarkets. You can get light refreshment (coffee, beer, snack) in San Gregorio. Pescadero has a couple of places where you can get a meal. Further south, at Gazos Creek, there is a full restaurant (and a gas station that sells snacks). The Costanoa Resort has food and groceries. Continuing into Santa Cruz County, there are restaurants and a convenience store at Davenport. If you plan to continue through Santa Cruz, be aware that the commercial section of Mission Street (Highway 1) is bike-unfriendly (take side streets).
I have biked this coast three times. The first, in 2007, was spontaneous. The weather forecast indicated a one or two day window of clear skies instead of the usual coastal fog. So I arose early, and biked down from Bonny Doon to Davenport, then took the bus to Waddell Creek. That stretch is interesting by bike, especially if you take the inland route along Swanton Road. But I had done that section before.
I biked northwards, with no particular plan. After a few minutes I was at the entrance to Año Nuevo State Beach, which has a seasonal nursery for elephant seals. But the beach wasn't open that early in the morning (it was not yet 8:00AM) and in any case it wasn't the best time for seals. So I continued along Highway 1.
At Pescadero, I turned inland, then took Stage Road to San Gregorio. This area is particularly nice for cycling. The photo below (taken on my second ride, when it was foggy) doesn't do justice to the expansive rural view from the crest. Stage Road has hairpin turns, so be careful lest you drift into the oncoming lane there.
I continued north to Half Moon Bay. By then it was just past noon, so I had lunch and watched a soccer game at the pub. Then, I biked back to Davenport in time for the early evening bus up the hill to Bonny Doon. Round trip, about 85 miles. At my age, not everyone can do that. But a friend from Santa Cruz happened to see me up in Half Moon Bay, so I can prove I did it.
In 2008, I did it again, this time continuing northward to San Francisco and eventually Point Reyes. I took the afternoon bus to Waddell Creek, then biked a few miles to the Pigeon Point Lighthouse hostel, which was the real starting point for the journey. The next day, I re-traced my route to Halfmoon Bay. But this time, it was foggy, with a strong headwind all the way. Understand that on any summer day, the wind is from the northwest, roughly parallel to the coast in this area. If you bike here, the smart way is from north to south, not south to north as I did. However, it is often the case that the wind is low in the morning hours, and I had planned to bike northwards only in the morning. Bad choice.
I biked to the Point Montara Lighthouse hostel. It is located in a fine nature area, paticularly for urban visitors who don't have as much opportunity to be "at one with the coast" as I do. Near Point Montara is a beach nature reserve. A group of harbor seals was resting on the beach. It's a no-no to approach resting seals, since they will slither away if you approach, and they need the rest. Orange cones mark the safe distance. Can you see the seals in this photo? If not, click the photo for an enlargement. In the center, one seal has his head up.
My destination was San Francisco, then later onwards to Marin County. But when I got to Montara, it was still foggy and windy, so I put my bike on the bus to Daly City, then another bus to downtown. When the bus went through the "Devil's Slide" section of Highway 1 (between Montara and Pacifica) I noted that I wouldn't like to bike through there. The road is hilly, winding, without much shoulder in places, and heavily trafficked. Others tell me that the section is open to bikes, but I can't see why.
On my third trip, I took public transporation to San Francisco, to hear "Opera in the Park." Then I biked back, from Golden Gate Park to Waddell Creek, with one stop at Montara. I bypassed Devil's Slide using San Pedro Mountain Road, a deteriorating former road that is no longer open to vehicular traffic in most places. Due to its crumbling pavement I wouldn't recommend it for road bikes with narrow tires, and I definitely would not bike it in the dark, even with lamps. The road winds its way over a ridge, reaching peak elevation of about 900' (versus about 500' for Highway 1 there). But the grade is sufficiently gradual, particularly when approached from the north, that it is not a major challenge.
To get to San Pedro Mountain Road from Highway 1 at the south end of Pacifica, turn inland at Linda Mar Boulevard. In about a mile, turn right at Adobe Drive. In half a mile, go left at Higgins Way. You will see a sign indicating that Higgins way is not a through road. At the end of Higgins Way there is a barrier. San Pedro Mountain Road is the partially paved path. To get to San Pedro Mountain Road from Highway 1 from the north end of Montara, pass the flat area with Montara State Beach and the farm. Just as the highway is about to enter a cut in the cliff, look for a yellow gate with a gravel road inland. About half a mile along that road, you will encounter a building (I believe it has horse corrals). There, take the road going left, uphill. You can look at the areas on Google Maps.