After a few years of cruising, you will get a good idea of the things that fail, and you will learn to carry spare parts and consumables. Fluids, belts, gaskets, nuts and bolts, screws, gaskets, various bits of hardware, wire, light bulbs, butt connectors, crimpers etc. In addition, you should carry a full tool kit to fix just about anything on your boat. This should include basic tools for plumbing, electrical, mechanical, woodwork, fiberglass and metal work. When things go wrong it will come down to you, your tools and your knowledge.