As you're English, I dont know how much you'll appreciate the obvious stuff, like Bannockburn, the Wallace Monument, etc... it's all pretty 'rah-rah Scotland'! It's a beautiful place, but they do play up the nationalistic stuff quite a bit.
Hummingbird lived in Stirling for awhile, so she might be able to tell you about good pubs, restaurants, etc.
The Wallace Monument is definitely worth seeing, as is the Stirling Uni campus -- it's got a man-made loch right smack in the center of it, with all sorts of ducks and geese you can feed. Watch out, though! Once those wee birdies smell bread, they'll descend upon you in droves!
As for restaurants and pubs, Papa Joe's in the town centre is good (Italian and assorted burgers, sandwiches as well), and there is a fantastic curry house just up the street from there as well, but for the life of me can't remember the name of it. Also, Golden Lion Chinese restaurant is good. The town centre is very small, so you could really just have a walk around and see what takes your fancy. There's a trendy bar called Pivo's on Corn Exchange as well, which is nice for having a wee bevvy.
The local shopping centre is called "The Thistles" and has your full-range of high street shops (Debenhams', NEXT, River Island, etc.) There are also some specialty shops along the high street where you should be able to buy Scottish gifts.
Nearby towns that you could have a wander in include Bridge of Allan (several nice shops to poke around in) as well as Dunblane, which has a cathedral. I used to work at the Hilton there and they have a silver service restaurant, if you're looking for a more upscale setting for dinner. You do not need to be a guest at the hotel to have dinner there, although I'd advise booking in advance.
Will you be driving? If so, might I suggest taking a jaunt to Callander? I think it's about 40 minutes' drive (maybe less?) from Stirling, and has loads of crafty type shops, and places to get really nice ice cream and sweets. The drive there is very scenic as well.
Stirling's a very nice place, and should make for a nice day out. Enjoy your trip!