For torch type front lights the Fenix Lockblocks ([url=http://www.fenixtorch.co.uk/led_torches/lockblock.html]here[/url]) are good for fitting most securely to your bars, any size bars too. I've got a couple that I've used and never had a problem, simple velcro fitting so easy to whip on and off too
.
Re the chaingangs, for what it's worth I would suggest:
- have a couple of routes to try out and see what suits the type of training ride you want to do best, if not a full on CG then you could use different roads which may not be suitable to a CG. Simple out and back or left, left, left routes of a circuit then anyone can pick up where they are if dropped or chase on if a late arrival.
- fix a date for the first one, turn up and do it. If it's 2 people doesn't matter but it fixes a date/day of the week in minds. May take a month or two to pick up but if at least 2 can do it each time then it starts to set it in stone and folk can just turn up if they're free without having to do a big check-up first.
- specify the type of group it'll be so if you are a 18s CR standard doing a training ride then if someone from the 19s or TG wants to do it fair enough but not to disrupt the "tin" of the training ride. An 18s rider won't get much training benefit from someone destroying their legs in 5 minutes so faster riders could do longer turns rather than much faster turns.