My student card from Worcester worked at pretty much everywhere, and obviously was free. The only place that has been arsey about it is Rymans, which get you to sign up to their 'Student Genius Club' to get 10% off. HOWEVER, if you have an NUS card, use that and you'll get 12.5% off, without signing up with Rymans
I'm with Lloyds for my student account, and get an NUS card free for 3 years. Had some trouble sorting it out, but managed to get one eventually
Hardly used it when I had my university card, so if you have to buy one, just whether the places you usually shop at accept student cards for discount (if they do, probably not worth getting an NUS card). There's UniDays you can sign up to for online discounts, but I've never used it, and there's also a few other card schemes, such as The Student Card, but tbh I'd just stick with your uni card and/or an NUS card, as these are more likely to be accepted