Horseback riding can be a dangerous sport. Riding safely means staying comfortable and not letting injuries ruin your fun. Safety equipment won't keep you completely injury free, but in the case of an accident, may help reduce the severity of injuries. Wearing and using things like a helmet, riding boots, a crash vest, and safety stirrups can make your ride a lot safer than going without any of those things.
If you invest in no other piece of equipment, you should at least buy a riding helmet. Head injuries aren't completely avoidable, but many can be lessened or circumvented altogether through helmet use that fits well and wear it every single time you ride to protect your head and brain.
Safeties vests help protect your torso if you fall. Crash or safety vests help prevents injury to your internal organs, your spine and your ribs. These heavily padded, but lightweight vests are commonly worn by rodeo riders and eventers. More often, crash vests are seen on long distance riders, jumping, pleasure riders, and speed games competitors. They can be hidden under dressage jackets. Pleasure and trail riders suggest wearing a quick-dry top underneath the vest if you're concerned about it being too hot during the summer. Eventers wear them under a colourful jersey. There are a few different styles, and they do come in different colours so you'll want to try a few on before buying one. One style has an air system that is triggered when the rider is ejected from the used saddles. Some are suitable for ATV, dirt bike and horse riding and all come in kids as well as adult sizes.
Boots serve two purposes. A riding boot with a small heel will help prevent your foot slipping through the stirrup and provide some protection if your toes get trampled. Tall boots also protect your leg from chaffing while you ride and from getting scraped by branches and shrubs as you trail ride.