Have you asked about a day pass? They used to do one so that you could have a look around the store (you couldn't make a purchase though). That may be worth enquiring about but as I say, I'm not sure if they still allow that.
They have an excellent bakery section. They also make celebration cakes to order and the prices throughout the bakery section are very good.
Different stores have more or less range depending on their size. The store I use has a photo processing lab on site. They also offer the poster size prints. Again, all at competitive prices.
During the summer months they stock a few 'outdoor activity' type goods such as canoes, tents, bikes etc. During the winter months they have a selection of toys and Christmas decorations.
They always have a good cross section of books and the prices are usually competitive.
There's a small range of clothing such as jeans, coats, etc and again they can be competitively priced.
I personally find that the beers, wines and spirits aren't worth it. Supermarkets usually beat them due to the deals they offer.
The freezer section has some good prices on products such as lobster, prawns, steaks etc.
One BIG bonus that I think makes it worth the membership fee is, they offer a 90 day return policy on TVs and a 5 Year Warranty comes with the TV as part of your membership. Obviously if you chose to discontinue your membership the warranty ceases at that point. They also demo all of the TVs they sell so you can see them in action. Once a TV range has sold through they sell off the demo models and if you're in at the right time you can get a very good bargain. And yes, even an ex-demo TV comes with the 90 days return policy and the 5 year guarantee.
With Christmas approaching it may well be worth the investment. My personal opinion is that it is worth the £30 fee but no doubt there'll be some who disagree.
Hope that helps.