Most don't go for anything more advanced than a vodka coke, tbh. I do know a few people who make proper cocktails at home for pre-drinks, but that's seen as a treat because the additional ingredients can make it quite expensive. "Proper" cocktails are invariably too expensive (£6 for one glass? Not affordable!), hence students will go for cheaper options like a vodka mixer.
However, Wetherspoons do some cocktail pitchers (£6 or so per pitcher, which includes 4 shots, and then the option of an extra 2 shots of vodka for £2) which are eternally popular with students.