You can buy one of the readily available save a dive kits or assemble your own set. The exact contents of a save a dive kit depend on the gear you carry and the diving you do, so there is no universal list of necessary parts. However, some things, such as extra fin and mask straps, tank valve o-rings and a regulator mouthpiece should be in most, if not all, kits. Your kit should also include snorkel-keepers, clips, and lanyards, silicone lubricant, weight keeper, mask anti-fog, cable ties, spare batteries, etc.
It is also recommended that you carry a basic tool kit in case you need to make some emergency repairs. Some of the most commonly used scuba tools include hex wrenches that fit 1st stage plugs, wrenches for dive hoses, as well as flathead and phillips screwdrivers. Side/angle cutters, at least one adjustable wrench and an 8 mm Allen key for DIN/Yoke valve removal will also come in handy. If you don’t want to carry a full-sized tool and repair kit, you can always purchase a compact scuba multi-tool.