I have several backpacks of different sizes for different situations. I don't have a car, so anything I buy has to be carried home. If it is going to be very heavy, I either take a wheeled shopping trolley or I get a delivery. Most used backpack is a 12 litre one, which takes a few books, a camera, a comb and lipstick, purse, gloves and a knitted hat. In it I keep a couple of plastic carrier bags for overflow. My emergency nylon shopper, kept in an ordinary shoulder bag for unexpected shopping, is a featherweight fold-up nylon back pack which cost me £4.95 and takes up hardly any space. Very handy for unexpected purchses when I have a conventional handbag with me. For events which involve a fair bit of walking around carrying bits and pieces, but no shopping, I have an M&S black leather backpack.