The GHG Protocol divides scope 3 into 8 upstream categories (purchased goods and services, capital goods, upstream energy, upstream transport, waste, business travel, employee commuting, leased assets) and 7 downstream categories (downstream transport, processing, product use, end of life, downstream leased assets, franchises, investments). Category 1 (purchases) is almost always dominant.
Read the source article: Scope 3: definition, 15 categories and calculation method