While the legal requirements will vary based on the type and size of your dinghy, typical safety equipment includes a life jacket of the correct size for each person, a sound-producing device (air horn, whistle), bailer, and, if operating after dark, proper navigational lighting. A throwable floatation device, such as a buoyant seat cushion, is also good to have.
Dinghy Grab Bag
The key to ensuring your dinghy is properly outfitted every trip is to make placing required gear on board as easy as possible. A life jacket bag makes it easier to toss and store them on board. Similarly, a dinghy "grab bag" containing the rest of the necessities will keep everything organized and easy to carry.
Any noncorrosive, buoyant, watertight box or container of suitable size can serve as a grab bag. Dry bags or smaller abandon-ship bags (usually constructed of nylon and padded with foam) also work well. Regardless of what type or style you choose, make sure it's large enough to carry what you need and that it floats with everything inside. Secure or attach it to the dinghy with a lanyard so it doesn't float away if you capsize.
What To Bring
Next up is outfitting your grab bag, which could also rightly be viewed as a mini ditch bag. My dinghy grab bag contains a hand-held VHF radio, signal mirror, whistle, flares, flashlight, several light sticks, tape, multipurpose tool, small first-aid kit and a couple of space blankets. I also carry a small tool pouch with spare spark plug for the outboard (and the wrench to change it) as well as a handheld compass in case the fog rolls in, making a trip back to the boat interesting. Additional items, such as sunblock, a bottle of water, and maybe a few energy bars might come in handy as well. Cellphones are a good item to have, too, but should not be considered a replacement for a handheld VHF radio. Get creative and customize the contents of your grab bag to meet your particular needs, but avoid making it so bulky that you have an excuse to leave it behind.
Pumps And Bailers
Always have some method of dewatering your dinghy, be it a bucket and sponge or that old standby, the venerable "plastic jug with the bottom cut out" scoop. A small hand pump (such as the old naval piston type) mounted inboard of the transom works well, too. Like the grab bag, your bailer should be secured to the dinghy to prevent loss in the event of a capsize.
Regardless of how you power your dinghy (outboard, sails) always carry a pair of oars or at least a paddle. Ensure oarlocks are of adequate size and strength. Unless they're self-locking, it's also a good idea to have a light lanyard securing each oar to the dinghy to prevent loss while rowing. The oarlocks on some inflatable dinghies simply mount into a socket along the gunwales and tend to pop out fairly easily under anything but the lightest rowing.