In any event, here are the ideas, roughly in the order of my preference:
1. Gold Short. Gold is again butting its head against the psychological 1300 here, and its been sideways between 1200 and 1300 since mid-February, having previously unsuccessfully challenged the +1300 mark in early May before giving up the ghost all the way back to 1200 by May's end. A meaningful relief rally in equities on a Bremain vote may guide the precious metal lower.
Because I'm currently in a GLD position, I've chosen to close the put wing sides of my GLD iron condors, leaving short call verticals in place to take advantage of any downturn. If the short call verticals don't hit max profit outright, I'll merely wait and buy the dip by adding the short put wings back in if there's a significant drop in price.
Trades: GLD or GDX short call verticals above current resistance.
2. TLT short/TBT long. Traders have fled risk-on assets a little bit here in advance of the referendum. As with gold , they've sought out safe havens such as treasuries, driving TLT to within 5% of its 52-week high and TBT to within 5% of its 52 week low ( TBT is the inverse of TLT ).
Trades: TLT short call verticals above current resistance; TBT short put verticals below current support.
3. European Indices/Index ETF's Long. Naturally, you can play US equities indices long here, but since this is uniquely a European "thing," I would think you'd want to put plays in European indices or index ETF's to get the full brunt of the relief rally and not the spillover that will occur into US markets. Although the Euro index ETF's have already experienced a bit of resurgence off of lows, they may have further upside once the referendum is over.
Trades: EFA short put verticals below current support.
4. Cable Pairs. GBPUSD is the most obvious choice for a assumption, although it's already rallied from the 6/16 low by 200+ pips, although it may have another 350 pips to the upside in it (the 5/26 high).
In all of these instances, I would trade small and, if trading the underlyings directly, I would common sense in setting stops. Keep in mind that all these assets are likely to move "in tandem," so I would pick one to trade and not put on trades in the others. The reason my preference is for a gold trade is that (a) it's a mover; (b) it's already at resistance; and (c) well, to be honest, I've already got a GLD trade on that I can use to take advantage of the movement.