I ride my bike to pick up my groceries like most sane people.
That's great for you; single-person-urbanite-centric much?
I used to do the same when I was a student and lived relatively close to the supermarkets. A few years down the line, I/we shop for three people once a week. That can be a good forty kilos depending on what we buy.
A little more on topic - and perhaps more importantly, these grocery deliveries also save *time* - life's most important resource.