For lunch in Glossop, conveniently close to Magic Mountain, try either Barrista - good coffee, posh continental sarny-type things, a little more expensive than the Glossop average - it's on Victoria Street just before you turn left into the MM car park (from the carpark, turn right out of the main entrance and walk about 20 yards...) Or the Rainbow Bistro, which is more traditional and is right by the car park - head up the obvious steps and you'll walk straight into it. Technically it's on Glossop High Street, viz, the A57.
For Magic Mountain, if you don't know it, turn left at the main lights in the centre of Glossop after approaching from Sheffield then take the first left into the big carpark and head right down the far end, where they have free customer parking.