Although I always hate to miss putting on trades in a high volatility environment and generally don't like to exit setups merely because "something is happening," Brexit may be one of those special situations where it is likely that whichever way Brexit goes, the movement may be overly large, whether it takes the form of a relief rally on Bremain, or a significant downturn on Brexit vote ... .
Moreover, I would also like to devote some attention to plays in the non-US markets, so I'm watching the options playable Euro ETF's like FEZ (Euro Stoxx 50), HEDJ (Europe Hedged), EWG (Germany), EWU (UK), EFA (MSCI EAFE) and EWQ (France) (they basically all have the same trajectory; the question is which ones will be reasonably liquid to play via options ... ).