A sewing kit is the quiet workhorse of field repairs: a few needles, strong thread, some safety pins and usually a few spare buttons in a case that weighs almost nothing. It fixes the failures that ruin a cold or wet day out — a split seam letting the wind in, a torn rucksack strap, a burst trouser hem, a loose button on a coat you are relying on for warmth. A stitched repair is permanent, low-profile and holds through wash after wash, which is exactly what you want on clothing and load-bearing gear.
Duct tape does a different, faster job. It is a wide, aggressive-adhesive cloth tape that sticks to almost anything and holds under tension, so it patches, bundles and seals in seconds with no skill required. It shines on hard, smooth or wet-then-dried surfaces — a cracked water container, a split tarp, a snapped tent pole splinted against a stick, a blister padded before a long walk. What it will not do is make a lasting repair on fabric you need to flex, stretch or wash: on clothing it peels, leaves residue and traps damp. The two solve overlapping problems from opposite ends — one is slow and permanent, the other instant and temporary.