I'd rather not use wordpress (with wordpress-ecommerce wordpress plugin) or any other full-featured store scripts because my requirement is very easy and limited:
2 product types: bags, tees 3 groups: classic, modern, special 3 sort options: by color, by category, by cost Trolley with PayPal as payment processor.
Can there be any lightweight (and open-source) script that does all of this while permitting me to personalize the feel and look easily?
I believe this is actually the one you're searching for http://wordpress.org/extend/plugins/wordpress-simple-paypal-shopping-cart/
Very easy to use ) you may also begin to see the demo. However I fear it's no sorting option :(
If you do not mind using PayPal's shopping cart software:
Other ideas (not every free though):