The most-used bicycle safety equipment aside from helmets is probably the glove. Gloves protect the skin on the palms of your hands when you fall on pavement. Some are padded to protect the hands from compression stress from the handlebars on long rides. They keep your hands warm in winter. When you ride through a patch of glass they let you stop and wipe the glass bits from your tires before the glass penetrates the tread fully. (Don't try this while still moving!) Gloves are highly recommended. We like the washable ones for summer use. For winter we find that the ones with non-breathable membranes get wet on every ride, and have to be dried out thoroughly before another use or they turn rancid inside. Down mittens are the warmest thing we have found for winter, but they also get wet.
Many contact sports use mouthguards to protect the participants. That includes boxing, football and many others. There is evidence that blows to the chin do a lot more than mess up your teeth. Energy transmitted by the jaw joint can be channeled straight to the brain, producing the same effects seen in fighters when they are hit too hard. A good mouthguard or jaw-joint protector stabilizes the jaw by engaging both the upper and lower teeth. That can be expensive, or just a few bucks from a sporting goods store for a "boil and bite" that conforms to your teeth after heating briefly in boiling water. Most riders find a mouthguard confining because it can interfere with mouth breathing, spitting and shouting at dogs, cars and pedestrians. There are designs that have central vents to minimize those problems.
Full Body Armor
We have yet to see any full body armor for cyclists that would provide real impact energy management. The armor on the market is mostly designed to spread the effect of hitting something sharp. Nothing out there that we know of will really protect against broken collarbones, for example. Armor is confining and hot in warm weather. We think that parents looking to prevent an active boy from harming himself can do more with education than outfitting the kid with body armor!
We have received a tip from an "extreme freeriding" rider that armor has improved and that some riders credit it with preventing injuries in that sport. His advice:
Shin/knee armor does provided impact protection for high speed collisions. Additionally, body armor can save someone from broken ribs or vertebrae. Those who have fallen on their backs while wearing body armor and jumping over rocks or concrete stairs can attest to this... For most children this sort of gear is totally unnecessary, but for those select children who take interest in extreme riding, parents need an established source to consult for safety advice.
Low profile recumbents and others who are concerned about being out of sight in traffic often use a bike flag. Long distance tourists favor them for increased visibility on highways. They are readily available at big box retail stores as well as bike stores, usually in orange or white for high visibility. Do they drag? Some. Do you care? Maybe.
There is no substitute for active lights if you ride a bicycle after dark. No reflective device or material can achieve the visibility that electric lights can achieve. We use the largest headlights we can, plus the typical blinking rear lights that identify a bicycle as a bicycle, and always have some redundancy to accommodate the notorious unreliability of bike lights. Here is a page on the bike lights used by a member of our staff. Active lights unfortunately require active maintenance, but we think no rider should be without them at night. MH4>Horns We don't find that horns do much for safety on a bicycle. Your voice is faster to react and adapts better to different situations. The primal scream produces good adrenalin-based reactions in motorists and is probably your best defense in most bike/car situations. It requires no evaluation by the driver, since the panic in your voice is obvious, and it can move a car over a lane almost instantly. Curse words will not improve on that, by the way, since you will get a quicker reaction when the motorist is scared, not angry.
We use a lot of reflective tape on bicycles and helmets. But we recognize its limits: there is nothing to reflect back to a car until the car's headlights are shining on the tape. At that point it may be too late. And there is no scientific evidence that reflective material actually helps to either identify the bicycle, pinpoint its location for the motorist, or grab the driver's attention any sooner. Still, we would not be without it, since it does not rely on maintenance or reliability of the bicycle's lights. We often see cyclists at night because of the CPSC-mandated reflectors on their bikes even if they do not have lights.
Toe clips, clipless pedals and cleats
Under some conditions the rider cannot have their feet clipped to the pedals, but usually you can, and doing it helps to eliminate the crashes that result when a foot slips off the pedal at the wrong time. Whatever system you use must be adjusted properly and maintained well, or you will fall over some day because you are unable to get your foot out fast enough.
Bike tires are not all equal in adhesion to the road, particularly when conditions are rainy or icy. Tread may not be the answer, and a softer rubber compound may be more important. We don't know enough to advise you on brands or models, but you should be aware that tires can make a difference. You can identify the softer tread compounds by feel, or by asking a knowledgable bike shop employee. You want a tread that feels like pencil eraser rubber when the eraser is fresh.
A staffer here has not broken a collarbone since he bought a four wheel bike to ride when conditions are wet or icy. Here is a page on four wheel bike and tricycle sources.
The most important safety equipment on any bike is the brain of the rider. You can avoid more injuries by riding safely than equipment can possibly protect you against. Give it some thought, and make a conscious choice on the level of safety you want to pursue in your every day riding. Maybe you don't care that much if you are injured - - but maybe you do. Thinking about it in advance can give you behavioral guidelines for those occasions when some wild emotion or being late for something makes you want to throw caution to the winds! If you are an extreme freerider, you have already made your choice to pursue a dangerous experience. In that case, you will probably want to evaluate some extreme protection to go with your choice.