We’ve been on Saturday for the last 2 years and have bought grandstand tickets with camping for 2012 – can’t wait!
From what I have heard, you need to be up VERY early on race day to get a good GA position, so if you are doing the GA tickets you would probably be better camping. Your GA tickets will get you into any of the GA areas on Sat and Sun (see Silverstone website for position of GA areas) and roving grandstand access for Friday.
Drinking is fine, my husband has taken a cool bag of beers the last 2 years and there are also bars among the food catering stalls, those are not cheap though.
You don’t really need to take anything with you although we have taken our own food and drinks to keep costs down. Weather appropriate clothing/waterproofs/suncream are essential though! You might want to take ear defenders, although foam earplugs are available there for free. The noise is part of it for us so although the children had ear defenders (don’t take a child without them!!) we just used the foam earplugs for some of the time.