What people ride in is totally upto them, although I would never ride without at least a helmet, jacket, gloves and boots. I've been down the road in jeans n hoodie, and trust me, road rash kills!
Obviously you need a lid, I find AGV fit me perfectly while Arai don't. Head down to your local bike shop and try on every lid possible, different companies may have different measurements. I recommend you look at the Caberg lids, alot of commuters use em - they flip up and have an internal sun visor in them plus relatively cheap for a lid at around £100ish.
Jacket and trousers, you'd probably want textile, leather while giving better protection is heavier and less flexible. Textiles also tend to be a little bit better when it pisses it down. Recommend you look at the RST brand, I have a Spyke one myself. A lot of companies will sell matching trousers which zip together at the waist with the jacket. If you do take a tumble it stops them getting torn off and giving you bad road rash. My trousers slip over the top of my jeans so once I get to college I whip em off. They're definatley worth getting, jeans arent waterproof at all...however you can get some kevlar jeans for around £80 £130 if you're going somewhere social.
Definatley a set of gloves; Arlen Ness, RST, Alpinestars, Knox etc etc tonnes of companies to look at. Personally have a summer pair, cheap ebay buffalo ones (£30) and some random winter ones from the bargain bucket. Might be able to get some heated ones within your budget, keep hands toasty in the winter months. Try and get a neck tube too, stops getting a draught down your jacket...
Boots, your CCF army boots will do, any sturdy boot will with ankle protection.