Now come on able-bods, engage your brains. For starters, hanging anything from the back of a wheelchair, especially if it includes a few litres of milk, juice etc, will make said chair rather tippy — they're quite light these days you know. And secondly, three or four bags draped from one's handles tend to get caught up in one's wheels and spokes thus making it somewhat difficult for the chair to actually move, which is kind of the point. Duh!
Keep on rolling ... without shopping bags!