Buying too many functions you won't use
A 30-function multi-tool sounds impressive but adds unnecessary weight and bulk. Focus on the core tools you'll actually use: pliers, plain-edge blade, screwdriver, and bottle opener. Extra tools like corkscrews or miniature scissors rarely justify their presence in a survival context.
Never maintaining or sharpening it
A dull blade is more dangerous than a sharp one because it requires more force and is more likely to slip. Regularly oil the pivot points, sharpen the blade, and check that all locking mechanisms engage properly. Carry a small sharpening stone or ceramic rod in your kit.
Forgetting UK knife law
Under UK law, you can carry a folding knife with a blade of 3 inches (7.62cm) or less without needing a specific reason. Locking blades of any length require a good reason to carry in public. Ensure your multi-tool complies, especially if it has a locking main blade.