So I will be shooting a wedding reception in a gym in August. I haven't really done to much shooting in gyms. What would be the best lighting? Would just having an on the camera speedlite with a green gel on it be fine for moving around and off camera flash though an umbrella for portraits? If anyone has had experience shooting weddings in gyms I would love to here what you did.
What I've done is to use a speedlite on the camera and a couple speedlites on a lightstand which is manned by my assistant. (I use a Redwing Quickstand. No longer made, but this is very similar: http://www.cheetahstand.com/servlet/the-Cheetah-Stand/Categories)
I use the lights on the stand as my main light, with fill provided by the on-camera flash.
You could add a bounce/diffuser to your on camera speedlite for a softer effect: http://www.lumiquest.com/
However it sounds like you might be underequipped in which case you need to be honest with whoever is booking you. If it's a favour for friends let them know too as they may want to spread their bets. Don't turn up unprepared thinking you can do the job flawlessly in a situation where you have little control over the results and people are relying on you.