Of course I look to see what others are buying. People watching is the best thing about shopping! (I'll also happily offer my totally unsolicited advice if I see that someone is hesitating over buying a certain product, such as wine, that I happen to know about).
Of course it works the other way round too, in that I'm always conscious of what others might think about what I've got in my own basket/trolley.
I'm not so bad now though as I was when I'd just left college and was living on my own for the first time. I hated the idea of people seeing me with an empty shopping basket as I walked around the aisles, fearing that people would view as a young guy who didn't really know how to shop. So I always got something into my basket as quickly as possible after I'd walked into the supermarket. Since baked beans were the nearest things to the entrance, I always grabbed several cans as soon as I went in.
I only forced myself to stop doing that when I realised that I'd got over a hundred cans of baked beans (and not a lot else) in my kitchen cupboard!