The constraint is shape, not weight. A one-bag setup is limited by volume and by whether a thing can be squashed, and people optimise grams because grams are easy to measure.
A deck of cards weighs nothing and is rigid, which costs more space than its weight suggests. A soft pouch of watercolour kit is heavier and disappears into a gap. Worth thinking in terms of what packs around other things rather than what the scale says.