Favourite I've been on was Landyachting (Weston-Super-Mare). Admittedly nearly everyone there had been professional yachies or windsurf/sailing instructors who all took to it very quickly. 45mph down a beach was a blast.
I organised one for a mate last year:-
Friday night – got together at laid back campsite 1/2mile from Bat & Ball pub. Night in pub and mass fall of bikes on returning trip.
Sat am – Fly fishing. A bit left field but worked well with hangovers. Very few had done it before but a bit of relaxed instruction and bacon butties from the owner, and jobs a goodun.
Sat lunch – pub lunch and activites for the groom. Sent off to the corner shop in charity shop finest (repleat with p1ss stains) to buy the May issue of Milf monthly and a pocket pack of Kleenex (kept behind till) with 10p too little funds.
Sat pm – raft team building exercise. Nice bit of competition & lots of swimming on a boiling hot day.
Sat eve – Back at the campsite for a campfire. Cooked the fish from earlier and a barrel of locally brewed beer. Pretty mellow. Groom given wendy house to sleep in.
Sunday – 5 mile each way MTB along the SDW to cafe. Quick spin around QE country park "expert" route and return.
Sunday lunch – At the Bat & Ball pub, birth place of cricket for final pint and ploughmans in glorious sun watching the Hampshire WOMEN's cricket team play.
Stag party/weekend has to be right for the group and the groom but I think we got this one spot on for our gang.