Self bagging only pretty much where i live.
The cashiers at lidl are so fast it's hard to keep up.
I just stuff everything in fast as possible trying to maximise damage; this can also save on chewing time later.
But I only have to carry it as far as my bicycle - and I do sometimes need to fish out and reorganize heavy stuff at that point to keep the pain-ears vaguely balanced.
Though it is quite fun to try with 6-7 litres of liquids on one side and 2 carrots and a lettuce on the other.
If it's not too windy I'd just do that - shopping is boring.
If I was walking farther I'd take a big rucksack and yeah I'd probably pack it more systematically.
I can understand car users not bothering to organise though.
Unless you're driving 100km through the desert and think anything frozen wil melt.