Layering matters more than any single "must-have" item. Mornings on game drives can be genuinely cold, midday sun is strong, and Bwindi's forest interior stays cool and damp even in dry season.
For gorilla or chimp trekking specifically: sturdy, broken-in hiking boots, gardening gloves (the forest has stinging nettles and thorny vines), a light rain jacket regardless of season, and gaiters if you own them. Neutral colors are genuinely useful for wildlife viewing, not just tradition.
Beyond that: a warm layer for early starts, a wide-brim hat, reef-safe sunscreen, a basic first-aid kit, and a dry bag for cameras during launch cruises. We send a full checklist tailored to your specific itinerary once your trip is confirmed.