Depends on your budget really.
You can do the all singing all dancing stuff for £300-500 but that limits some of the mates from going, usually, or you can do a normal good day for about £100 now.
bear in mind that if it's a largeish group i.e. over 12 people then there will be lots of standing round waiting.
My recommendation from experience of doing my brother's a couple of weeks ago, is arrange to meet at someone's gaff in the morning, chill out, have a laugh, keep off the bevvies for now, just wind-ups and pass the time.
Then go off on an activity that everyone fancies, like shooting, quad biking, off-roading, karting etc (start asking people now what they like, don't leave it too long). Aim to do it in the afternoon.
Then go for a meal in a decent place that meets all/most peoples approval e.g. chinese, indian, mexican etc. Aim to start the meal around 7 or 8 so you can spend a good couple of hours having a good time with the meal, nice and relaxed.
Then those who want to go on drinking or clubbing can do so.
That's not to suggest an itenerary (sp) but is roughly how we did it, and a good guideline for a stag day/night that doesn't involve the tired old cliche of shit t-shirts, drinking til you're ill and potentially ending friendships.
EXCLUSIVE!!!

Shocking spy shots of GP superstar Valentino Rossi practicing for his new career in Covent Garden!
Only in your Super Soaraway Sun!