You can consider your trailer in isolation or you can factor in the tow vehicle and consider the two as a collective. The two indeed form a collective and hence you would have to look beyond the immediate or obvious trailer spares when you are shopping for parts and accessories. It is always advisable to have some trailer spares available when you are on the road or even if you are not venturing out. You never know when you would need to replace a part or accessory and it may be inconvenient for you to drive out to a nearby store and online retailers would not be able to provide you the trailer spares on the same day.
The most common types of trailer spares you would need are chassis and parts. You would need electronic trailer stabilisation, easydriver, auto adjust brakes, mudguards, tyres and wheels, attachment parts, supports, propstands, brackets, jockey wheels and accessories, lighting, device, anti theft gear, rope winches, equipment to secure cargo, loading ramp, storage box and toolbox among others. Depending on the type of tow vehicle you have, you will need a host of other accessories such as chains, backup alarms, chrome fittings, decals and graphics, safety equipment, mirrors and devices to measure temperature.
The other types of trailer spares are not very different from the usual parts or accessories you would need for automobiles. You would need axles and the various components including gears, kits, drive, steer, exchange, tag and pusher, belts and hose reels, air system, hydraulic system, clamps and hardware, compressors and valves for brakes, anti lock braking system, fluid and drums, dryers and lining, brake shoes and disc, spring, slack adjuster and pullers, suspensions, fan blades, drives, clutches, radiators and caps, thermostats and refrigerant, water pumps, clutches, driveshafts, vibration dampers, a plethora of electrical systems including alternators and batteries, cables and charging equipment, fuses and wiring, stands and jacks, welding equipment and winches among others.
Whenever you have to shop for some trailer spares, conduct a comprehensive inspection and check out if you need any other parts and accessories apart from those that must be replaced right now. You should check levelling valves, spacers, shock absorbers, dampers, springs and parts, coils, suspension parts, fittings, tire changing tools and lubricants among others. Do not forget to keep some bumpers, cargo heaters, collision parts, fenders, locks, landing gear, liners, mud flaps and hangers handy.