Getting a bicycle is probably the first thing that you need to do when you come to Davis. There are actually more bicycles than people here and the bike paths will lead you anywhere you desire in the city in a matter of minutes. However, Bikes also get stolen here quite a lot so make sure to lock it! There are several ways to get a bicycle:
Used bicycles for sale are frequently advertised on craigslist
A large collection of recycled bikes and part for sale can be found in Green Bicycle Depot
On-campus bike shop named Bike Barn
More bike stores across Davis are listed in DavisWiki
Also, every once in a while the university conducts an auction for abandoned bicycles. Information can be found here