Ask anyone who keeps a field-repair kit what they would grab first and you tend to get one of two answers, and they reveal how differently these two work. A multi-tool is precision in your pocket: a folding cluster of pliers, blades, screwdrivers, scissors and a saw that lets you grip, cut, tighten, prise and fix with actual mechanical control. It is the tool you use to do a job properly — to undo a jammed screw, snip a wire, tighten a loose fitting or open a stubborn tin — and a good one shrugs off years of use.
Duct tape is the opposite philosophy: brute-force improvisation. A roll of strong, waterproof cloth-backed tape does not do anything precise, but it will hold, seal, bind, patch and bodge almost anything long enough to get you out of trouble — a cracked window, a leaking pipe, a split boot, a broken pole, even a rough dressing in a pinch. It weighs little, costs almost nothing and needs no skill to use. One tool lets you fix things correctly; the other lets you fix things fast. In a real kit you want both, because the jobs they are good at barely overlap.