Have you tried carrying what equates to a toddler by one hand for 3km? Them plastic bag carrying handle bits are going to be digging into your fingers, friend. These days it won’t matter so much of course because the fingers will be frozen anyhow.
Frankly I haven’t used a shopping bag for years because I prefer collapsible cases (approx 40x60 cm) but economically those are even worse to carry farth than, say, 50m.