Picking a bike
Road bikes, mountain bikes, hybrids, cross bikes, touring bikes all work great - it depends on what works best for you.
A rear rack and panniers, a basket on the front or a backpack all work well. Many commuters use panniers, although baskets and backpacks may be more affordable options.
Full fenders are recommended, especially for bike commuting in Oregon! They will keep you dry and keep mud, dirt and debris off of you.
Headlights are mandatory at night; white in front with a red light in back. Wear bright or reflective clothing. You may also want to wear reflective ankle straps (which also keep your pants from getting caught in the chain) or apply reflective tape to your helmet or bike.
For short commutes, you may want to just ride in your work clothes at a relaxed pace. For longer or more strenuous commutes, cycling specific clothing may be preferable. Use waterproof and breathable fabrics to stay comfortable and dry. Panniers oftentimes have compartments to store a change of clothes and toiletries. Having an ankle strap to keep your pants out of your bike chain is also important!
Always wear a helmet while riding your bike no matter what. Be predictable and follow the rules of the road
Tools & Spare Parts
Bring only tools that you know how to use; a pump is a necessity. You may also want to carry a multi-tool with allen wrenches, screwdriver and a chain tool; be sure you know how to use them
Carry a spare tube and patch kit at all times; keep another spare at work. Know the condition of your bike and its parts by inspecting it regularly. You may want to keep a few spare parts that need regular replacement at work
Use a high-security U-lock; don't wait until your bike is stolen to invest in a good lock. Lock your bike to an immovable object in a highly visible area. Secure both wheels and other components if they can be easily removed
Tire liners and flat resistant tires go a long way to help decrease flat tire occurrence. Replace tires when they are worn out; check pressure with a gauge and be familiar with how much air your tires lose each week