Helmet, eyewear, usually gloves. I need to replace my old clear safety glasses. The frame is too thick at the top and hinders my view from the drops on the road bike. I rode Sunday evening without eyewear and had to pick gnats out of my eyes a few times. Fortunately there was no traffic at all the entire 18 mile ride. But that distraction could have been bad in other conditions.

There are long sleeve jerseys and shorts with a bit more padding on the most likely contact areas -- shoulders, elbows, hips. Knee pads/braces that shouldn't hinder pedaling too much. Check the catalogs for mountain biking apparel.

Judging from injuries my friends and I have experienced the past year or so, the most common serious injuries from falling off the bike are broken clavicles (two friend this year alone, both younger than I), wrists/forearms (one friend broke both wrists/forearms in a fall), and bruised/cracked ribs (one friend, and myself). The fellow whose wrists/forearms were broken may also have had a head impact and concussion because his memory of the incident wasn't clear.

The most serious injury was a fellow whose femur was broken. But it was a somewhat unusual situation, a slippery patch of wet silt on a concrete low water crossing. I'm not sure but he may have struck the corner of the narrow concrete spillway. Those things are treacherous because the puddles and damp patches of soil are usually silt, slippery as ice when wet. I'm extremely cautious riding my hybrid through any of that stuff, and completely avoid them when I'm on my road bike with slicks.

I've seen surprisingly few knee injuries from falls. That may be an advantage to foot retention systems, whether toe clips or clipless. Retaining the feet during impact lessens the risk of knees striking where the most damage might occur.

It may also be that falls happen more quickly than we can react, so the rider doesn't have time to extend a leg or knee in an instinctive effort to prevent falling or reducing impact. While I see some advice claiming that we should be able to roll with a fall or move our bodies in a way that minimizes injury, I see no evidence that most humans are capable of reacting that quickly. If you watch slow motion videos of professional cyclists falling, usually things happen so quickly they cannot react in time to prevent anything. If they can't do it, what are the chances of us ordinary humans "rolling" to minimize impact at speed? Pretty much nil. I remember consciously rolling with the fall back in February to avoid impacting my shoulder, but that fall was at only 10 mph or so. On a street or in a race at 20 mph? Nope.

As we age our brains shrink a bit and bounce around more. We're at risk of concussions even without a direct head impact. My mom began experiencing the effects of concussions in her late 60s after falling without hitting her head. After the first incident, falling on her tailbone and cracking some vertebrae, she showed the symptoms of a concussion. After that her balance became dramatically worse and she began falling more often, each time showing more symptoms of concussion even though she hadn't stuck her head. Her doctor ordered her to use a cane for balance everywhere in the home and a rolling walker outside. MRIs, CT scans and other tests showed no evidence of major strokes, Alzheimer's, Lewy Body dementia, etc., and only some evidence of mini-strokes. Yet she's developed serious memory loss and cognitive impairment, somewhat similar to CTE symptoms experienced by boxers and impact sports athletes.

Any practical bicycle helmets won't prevent concussions, although the helmet may help a bit as the dense foam compresses before breaking, decelerating impact. Helmets are mostly to reduce the risk of open head and serious brain injuries. I regard them pretty much as the bicycling equivalent to boxing head gear. The head gear doesn't prevent knockouts or concussions. It helps reduce the risk of abrasions and cuts (actually splits from the skin being compressed against bone, mostly around the eye socket and forehead). Practical bike helmets that anyone would actually wear will offer similar risk reduction.